Cover Photographs: Clockwise from upper right: (1) The command and service module scientific instrument module bay viewed from the lunar module. (2) Photomicrograph of a thin section of the orange soil sample collected at Shorty Crater. (3) Orange soil on the rim of Shorty Crater with the gnomon in the background. The soil consists of small orange glass spheres as shown in the photomicrograph above. (4) Large breccia boulder sampled near the base of the North Massif. The boulder appears to have rolled down the massif and broken into five pieces. The lunar roving vehicle is parked to the right of the boulder.

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Foreword
The character of the Apollo 17 mission to Taurus-Littrow was such that it invited superlatives. By almost all measures, it was an immensely successful voyage of exploration: the greatest harvest of new scientific data, the most kilometers traveled on the surface of the Moon, the largest number of scientific experiments performed-both in real time, by a scientist on the surface, and by automatic instrumentation installed and left behind-the longest time spent on and around the Moon, and the greatest amount of lunar samples returned for study in laboratories all over the world. But numerical measures like these, pleasing though they may be to the thousands of us who had some connection with this mission, do not seem an adequate characterization of this sixth and last of the Apollo series of manned lunar landings. We cannot now be sure how history wilt assess this extraordinary enterprise. It may be that, from the perspective of decades, the Apollo Program will stand out as the most singular achievement to date in the history of man's scientific and engineering endeavor. From this perspective, seen without hubris, it may be seen that all of us will be remembered for having liw_d at the time of Apollo. It may be that, in days to come, Apollo will be perceived as a threshold for mankind from the planet Earth. Dr. James C. Fletcher Administrator National Aeronautics and Space Administration

Introduction
"'There is nothing more difficult to take in hand, or perilous to conduct, or more uncertain in its success, than to take the lead in the introduction of a new order of things. "" Niccolb Machiavelli

As the splashdown and recovery of the Apollo 17 crew marked the end of the Apollo flit_t program, this final volume marks the end of the. Apollo Preliminary Science Reports. From every aspect, Apollo 17 was indeed a fitting capstone to the Apollo missions. Its awesome and magnificent midnight launch, its flawless operation, its 72-hr lunar stay time, its deployment of scientific instrumentation, its return of the richest collection of lunar materials from any lunar site, its orbital science coverage, and its glorious splashdown in the Pacific Ocean surely marked Apollo 17 as the mission most impressively exemplifying the Apollo Program. The Taurus-Littrow landing site for Apollo 17 was picked as a location where rocks both older and younger than those previously returned from other Apollo missions and from the Luna 16 and 20 missions might be found. For this mission, it was hoped that the discovery of younger basaltic rocks, differing in crystallization age from the 3.2 to 3.7 billion years of previously returned mare basalts, would lead to an improved understanding both of volcanism and of the thermal history of the Moon. Similarly, it was hoped that the discovery of rocks formed earlier than 3.7 to 4.0 billion years ago would lead to further understanding both of the early lunar crust and of material present at the time of the formation of the Moon. The identification and selection of the landing site resulted from Astronaut Worden's Apollo 15 orbital observations (he noticed dark patterns that looked like cinder cones in the Littrow region of the Moon) and from detailed analysis of the Apollo 15 imagery, xiJi

The rim of the Serenitatis basin in the Taurus-Littrow region seemed to have all the elements geologists would want to explore in this final Apollo mission. Cinder cones and steep-walled valleys with large boulders at their base presented the possibility of sampling, at the same location, both young volcanic rock from depth and older mountainous wall material. Thus, the setting for the conduct of the Apollo 17 landing was a unique place in which to carry out many investigations and to return lunar materials that could aid in answering many fundamental questions. From the standpoint both of geologic features and of samples returned, the Taurus-Littrow region represents the most diverse landing site of the Apollo missions. Returned samples include a variety of mare basalts resembling those of the Apollo 11, 12, and 15 missions and Luna 16;avarietyofbreccias(including KREEP-like, anorthositic, and soft types) similar to those of the Apollo 14, 15, and 16 missions and Luna 20; two coarse-grained igneous rocks of a type not found on previous missions; dark mantle softs that appear to be erosional products of basalts; light mantle softs that appear to be dominantly the erosional products of highlands; a variety of exotic glasses; and, most characteristic of this mission, boulder samples that provide the best alternative to inaccessible outcrops of the lunar surface. At Shorty Crater, orange and black glasses that were hopefully young volcanic material were observed and sampled. However, the old age of the glass and the astronaut observations and photographs suggest that this impact crater apparently excavated layers of very old pyroclastic material. Throughout

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APOLLO 17 PRELIMINARY SCIENCE REPORT Several other surface and orbital experiments were conducted on the Apollo 17 mission, which include the lunar atmospheric composition, the lunar ejecta and meteorites, the lunar tidal gravimeter, the ultraviolet spectrometer, the infrared scanning radiometer, and the lunar sounder. At the time of this writing, there are insufficient data to give an overview from these findings, which, in the future, are expected to give additional information about Taurus-Littrow and that region of the Moon covered by the command and service module groundtrack. The sections that follow present the preliminary results obtained in the analysis of the Apollo 17 data to date. As will be seen, the Apollo 17 data fill some gaps in knowledge about the near-side surface of the Moon but, at the same time, raise many other questions. However, one cannot conclude a report on the Apollo 17 mission without again emphasizing that it was a fitting finale to the Apollo Program from the standpoint both of operations and of science. It is also important to review what has been learned in the brief 3.5 yr from the first lunar landing of Apollo 11 on July 20, 1969, to the final splashdown of Apollo 17 on December 17, 1972. Before the Apollo Program, astronomical observations provided an early picture of the details of the lunar surface. In those days, intelligent speculation about the origin and history of the Moon was greatly inhibited because the scientific data required about the chemistry and about the internal condition of the planet could not be furnished even by the most powerful telescopes. Some of the most important scientific observations concerning the nature of the Moon and existing prior to the manned lunar landings are summarized below. The discovery of the physiographic features of the Moon dates back to Galileo, who observed that the side of the Moon facing the Earth consisted of mountainous regions that he designated terra and smoother regions that he designated mare, similar to terrestrial continents and oceans. He also observed a marked difference in reflectivity between these two regions of the Moon: the mare was much darker than the terra. Further astronomical studies added much detail to Galileo's discovery, including rather fine features such as tire rilles. However, before Apollo, the cause of these fundamental physiographic differences was not well understood. Later, some scientists hypgthesized: that the relatively smooth mare basins were very extensive lava flows. Others theorized that

this landing site, 10 to 20 percent of each soil sample consists of these "exotic" glasses, apparentIy brought from subsurface layers and distributed by the gardening effect. The Apollo 17 mission provided the scientific world with the best lunar sample return in both potential quantity of information and variety of sample types. Except for the sampling of one possible outcrop on Apollo 15, the Apollo 17 boulder samples should allow the best possibility of placing returned lunar materials in their proper structural and stratigraphic context. One example of how sampling techniques have become more sophisticated since the Apollo 11 mission was the collection of samples from a large boulder at station 6. One part of the boulder was vesicular and green gray; the other part was practically nonvesicular and blue gray. Samples were taken from both parts of this boulder, as well as from various locations up to and through the contact, Further analysis suggests that the blue-gray material reacted to become more vesicular near the contact; this material also occurs as fragments within the green-gray material on the vesicular side of the contact. Sampling of this type provides insight into the evolution of the older crustal materials. Knowledge of the Moon was also enhanced by the correlation of the traverse experiments, which provided better understanding of the site's subsurface relationships, obtained from the interpretation of seismic, electrical properties, and gravitational data. Seismic traverse experiments indicate that basaltic flows extend to a depth of approximately 1.2 km. The traverse gravimeter experiment has provided limits to the density of the underlying material, and the observed gravity anomaly allows development of a model for mass variations in the valley and in the massifs. This model may be of significance in interpreting the major mascons of the Moon. The electrical properties experiment has confirmed the gravity and seismic data bY establishing that the basaltic thickness is between 1 and 1.5 km. These data also show that the regolith is relatively, thick, perhaps 20 to. 40 m. with some variation in thickness. The dielectric constant and loss tangent measurements are in good agreement with previously determined values obtained from lunar samples and ground observations, The heat flow measurements at the Apollo 17 site have been shown to be roughly the same as those at the Apollo 15 site, indicating that, at least on.the near side of the Moon, a reasonable value of heat flow may be 2 X 10 6 to 3 X 10 -6 W/cm2/sec.

INTRODUCTION they were extensive dust deposits, in fact, dust bowls. Still other scientists seriously suggested that the maria were filled by a type of sedimentary rock that was deposited at a very early stage in lunar history when the Moon had an atmosphere, Before man landed on the lunar surface, two explanations for the origin of the circular depressions or craters, the most common physiographic feature on the lunar surface, were continuously debated: (I) that the features of the craters, similar to calderas on Earth, were of volcanic origin, and (2) that the craters were produced by projectiles impacting the lunar surface, in the same way that meteorites occasionally excavate craters on Earth. Now it is fully realized that the surface of the Moon could be sculpted both by impacts and by volcanic craters, but primarily by impacts, Dialogue on the activity of the Moon and on the role of volcanism on tile lunar surface developed into three schools of thought on the therraal history of the Moon. One school held that the Moon had been relatively inactive and had undergone some chemical differentiation only very early in lunar history, Another school propounded that the history of the Moon was similar to the Earth's long and continuous record of volcanism and chemical differentiation, and that lunar volcanoes were active in the recent past. Others thought the Moon had undergone no volcanic activity at all. The chemical nature of the lunar surface, up to the time of Surveyor V, was totally unknown. However, there had been a number of suggestions. For example, it was suggested at one time that carbonaceous chondrites were typical of the dark mare regions; others suggested that meteorites known as eucrites were representative of the lunar surface; still others suggested that silica-rich glass found in mysterious objects called tektites must represent parts of the lunar surface. One could not even be sure that these hypotheses were mutually exclusive, The pre-Apollo data obtained by unmanned satellites discovered (1) the mascons, which suggested a remarkedly rigid or strong lunar interior; (2) either a very weak lunar magnetic field or no field whatever; and (3) a physiographic difference between the lunar far side and the near side, in that the dark mare regions were essentially absent from the far side of the Moon. As we now look back on the six Apollo landings, we are infinitely richer in facts concerning the Moon.

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Some of these facts and observations have already been tentatively assembled in models that are leading to a much fuller understanding of lunar history. Although it is extremely difficult to account for the remaining facts with a consistent explanation, major areas of understanding can be briefly outlined. A rather definite and reliable time scale for the sequence of events of lunar history has been deycleped. It has been established with some confidence that the filling of the mare basins largely took place between 3.2 and 3.8 billion years ago. This has been demonstrated from analysis of the mare basalts obtained from the Apollo 11, 12, 15, and 17 missions and Luna 16. Because these mare fillings represent a major physiographic feature on the lunar surface, it has been inferred that the time of formation of more than 90 percent of the cratering on the Moon was 4 billion years ago or earlier. In comparison, the ocean basins of the Earth are younger than 300 million years. (Terrestrial rocks older than 3 billion years are almost unknown.) The analysis of the highland material collected on the Apollo 14, 15, 16, and 17 missions and Luna 20 has shown the widespread occurrence of breccias with an apparent age of 3.8 to 4.1 billion years. There is strong circumstantial evidence that rocks dating back to 4.5 to 4.6 b/Ilion years ago must exist within the Moon, although very few of the Apollo rocks have crystallization dates lying between 4.0 and 4.6 billion years. It now appears that heat from the intense bombardment of the lunar surface by projectiles, ranging in size from microscopic to tens of kilometers in diameter, was effective in resetting most of the clocks used to determine the absolute age of the rocks. The relative importance of volcanic and impactproduced features on the lunar surface appears to be well established with the conclusion of the Apollo missions. There seems to be almost unanimous agreement that the dark mare regions are underlain by extensive lava flows, shown both by rocks returned by the Apollo 11, 12, 15, and 17 missions and Luna 16 and by the high-resolution photographs that give convincing pictures of features comparable to terrestrial lava flows. Almost all craters appear to be caused by impacting projectiles, thus leaving the question of volcanic rocks in the terra regions unanswered. With the conclusion of Apollo 17, it has been suggested that volcanic activity in the highland region subsequent to approximately 3 billion years ago may be highly restricted or virtually nonexistent.

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APOLLO 17 PRELIMINARY SCIENCE REPORT prove to be characteristic of the Moon, perhaps the explanation is that the Moon is richer than the Earth in the radioactive elements uranium and thorium and that these elements are strongly concentrated in the upper parts of the Moon. Two current theories of lunar evolution have resulted from the consideration of information concerning (1) the concentration and location of radioactive materials, (2) the inferred volcanic history of the Moon, and (3) the inferred upper limits of intemal temperature. The first hypothesis is that the planet was chemically layered during its formation. The low initial temperature of the lunar interior (below 500 km) gradually increased, perhaps reaching the melting point during the last billion years, while the initial hot temperature of the lunar exterior gradually decreased. Volcanism is entirely accounted for by early melting in the outer 400 km of the Moon. The alternate model of thermal evolution assumes that the Moon, chemically homogeneous during its formation, underwent extensive chemical differentiation that resulted in surface concentrations of radioactivity very shortly after its formation. In other words, much of the Moon was molten at its origin. Of course, both of these theories will undergo discussion and revision in the coming years. The most extensive and diverse data obtained on the lunar surface are concerned with the chemistry and mineralogy of the surface materials. The study of samples from the six Apollo sites and the two Luna sites reveals a number of chemical characteristics. Although it is very early to generalize from these relatively few samples of the whole lunar surface, two orbital experiments provide excellent data regarding the regional distribution of various rock types: the X-ray fluorescence experiment and the gamma ray experiment. The X-ray fluorescence experiment defined the prime difference between the chemistry of the mare and highland regions. The mare regions have alumihum concentrations 2 to 3 times lower than those of the terra or highland regions and magnesium concentrations 1.5 to 2 rimes greater than those of the terra regions. These differences in chemical concentrations throughout the equatorial region of the Moon are consistent with the chemical analysis of the returned samples. When orbital data and lunar sample data are combined, they provide an excellent explanation of the morphological and albedo differences. For example, all mare basalts have been found to be

Apollo experiments invesrigating whether the Moon is "alive" or "dead" indicate that, compared to Earth, the Moon is seismically quiet. However, there are many very small quakes, possibly triggered by tides, at approximately 800 km below the lunar surface. Below 1000 km, the Moon is partially molten. A quiet Moon is consistent with the conclusion that volcanism and other types of tectonic activity have been rare or absent from the lunar surface for the last 2 to 3 billion years. Lunar seismology reveals that the Moon has a crust more than 60 km thick. Both the precise origin of this crust and the compositions causing the discontinuity in seismic velocity are still subjects of debate. From the Apollo Program, we can conclude that the Moon, at one time, was very much alive and now is very quiet, The overall magnetic field of the Moon has been found to be negligible, as was thought before the Apollo missions. However, the magnetometers placed on the lunar surface reveal surprisingly strong local fields, variable both in direction and in intensity, Paleomagneric studies have also determined that mare lava flows crystallized in a magnetic field that was much stronger than that of the present Moon. These discoveries raise the possibility that, during its early history, the Moon either was exposed to a relatively strong interplanetary magnetic field or had a magnetic field of its own that has since disappeared, The interior structure of the Moon and its thermal characteristics have been investigatod through a careful study of the fluctuations of the magnetic field induced by the solar wind, which reveals a relatively low lunar electrical conductivity. The conductivity of most silicates is, to the first order, a function both of temperature and of chemical composition (such as the abundance of ferrous and ferric iron). With preliminary measurements from the Apollo 12, 15, and 16 missions and with fluctuation measurements of the magnetic field, lunar conductivity can be derived. In conjunction with various chemical models of the Moon, this conductivity can be used to place constraints on the deep lunar interior temperatures, which are highly model dependent, The thermal history of the Moon was investigated on the Apollo 15 and 17 missions through measurements of the heat escaping from the Moon. These measurements indicate that the energy flux escaping from the Moon is approximately half that of the Earth. This is surprisingly high, considering the relative size of the two planets. If these measurements

INTRODUCTION unusually rich in iron and sometimes rich in titanium, The high iron concentrations in the mare, as opposed to the low concentrations in the highlands, is a basic explanation of the albedo differences, hecause both glass and mineral substances rich in iron and titanium are usually very dark. The orbital gamma ray experiment results show that the region north and south of the crater Copernicus is remarkably rich in radioactive elements, A band going from north of the Fra Mauro site to west of the Apollo 15 site contains soil 20 times richer in uranium and thorium than either mare or terra in other parts of the Moon. The existence of a rock rich in these elements was also inferred from samples from the Apollo 12, 14, and 15 missions. The differences between lunar rocks and terrestrial rocks are so marked that the Moon must be chemically different from the Earth. The Moon appears to be much richer in elements that form refractory compounds at temperatures of approximately 1600 to 1800 K. Many scientists are now coming to the conclusion that the chemistry of the lunar surface reveals that some separation of solid material and gas in the lunar dust cloud took place at temperatures in excess of 1600 K. The strong depletion of elements that are volatile at high temperatures in the outer portion of the Moon is consistent with the enrichment of refractory elements, None of the three theories regarding the origin of the Moon-separation from the Earth, capture from a circumsolar orbit, or formation from a dust cloud surrounding the Earth-can be absolutely eliminated by the present data. However, the chemical differences between the Earth and the Moon, the depletion of volatile elements, and the enrichment of refractory elements in lunar samples make it unlikely that the Moon was tom out of the Earth. In summary, the age of the Moon is well determined, and the Moon has a crust (the chemical composition of which is fairly well understood), a mantle, and a partially molten deep interior. The understanding of the mascons is well underway. Facts substantiating the early theories of the atmosphere have been obtained. Basic questions that were asked 5 yr ago, such as whether the Moon is hot or cold, alive or dead, or has craters formed by volcanism or impact, are no longer asked. Apollo data have changed the types of questions asked. Post-Apollo questions are more detailed, more specific, and more

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sophisticated. Yet, despite the great strides taken in knowledge about the Moon, its origin and formation are still unknown. A storehouse of resources has been returned from the Moon: almost 385 kg of lunar materials (obtained from six different landing sites on the near side of the Moon), 37 drive tubes, and 20 drill stems. To date, only 10 percent of this lunar material has been examined in detail. Approximately 33 000 lunar photographs and 20 000 reels of tapes of geophysical data have been collected. Thus, in 4 yr of lunar exploration, our knowledge of lunar characteristics has been substantially increased, and vast resources of scientific data have been collected that will lead to a decade of data analysis. In the past decade, there have been two revolutions in planetary science studies. There has been a revolution in the new global tectonics describing the motions of continents and the generation and destruction of the sea floor. In its investigations of the origin, history, and formation of the Moon, the Apollo Program has led to a revolution in providing the first deep understanding of a planet other than the Earth through the development of new techniques of exploration, investigation, and analysis and through the integration of the scientific knowledge gained in interdisciplinary fields. The Apollo Program has provided Earth scientists with 4 yr of anxiety, excitement, and fulfillment. Apollo lessons may force a reconsideration of many of the techniques and models that are currently used in understanding the early history of the Earth. As we look to future generations, hopefully, we have developed a scientific program that carded out worthy and substantial preliminary investigations and that laid a very firm foundation for future scientific inquiry. In decades to come, the analysis of Apollo data may indeed lead to a polar orbital flight around the Moon or to a lunar base where men may explore the entire surface of the Moon. By studying the Moon, we can better understand processes of planetary accretion, evolution, and composition so that lunar studies have implications that extend beyond the Moon. Hopefully, our generation has performed a job that history will recognize as a commendable scientific endeavor, a contribution of valuable information-useful, meaningful, and inspirational. Anthony J. Calio NASA Lyndon B. Johnson Space Center

1. Apollo

17 Site Selection
N. W. Hinners a :_

Consideration of an Apollo 17 landing site began in earnest during debate over the Apollo 16 site, primarily because the Apollo Site Selection Board (ASSB) desired to consider Apollo 16 and 17, the last lunar missions, as a complementary paiL.Therefore, in order to put the Apollo 17 site Selection in context, it is necessary to discuss highlights of the Apollo 16 site selection as well. (For more details about the Apollo 16 site selectioni:see ref. 1-1.) Some of the content of this report is abstracted or paraphrased from the minutes of the ASSB meetings (written by the author) or from other unpublished documents (also written by the author) used as background material for or documentation of several meetings of an Ad_HoC Site Evaluation Committee. All that material is available on request. PRE-APOLLO 16 SITE S E LECTI O N STATUS At the time of the Apollo 16 site evaluation, soon after the Apollo 14 flight, there was a clear consensus among the lunar science community that both the Apollo 16 and 17 missions should be targeted to highlands sites. The Apollo 15 mission had not been flown, but the mare region adjacent to PJma Hadley and Montes Apenninus had been selected as the Apollo 15 site. Only minor support existed for another mare mission, and it was mainly limited to the Marius Hills. That candidate site, however, became largely academic when a revised launch schedule resulted in the Marius Hills being operationally inaccessible, or only marginally accessible, for either the Apollo 15 or 17 time frame. After imposition of the operational constraints, mainly accessibility and available photographic coverage, and after consideration of the scientific return, aNati0nal Aeronautics and ington,D.C.
Space

Descartes and Alphonsus emerged as the prime highland contenders for the Apollo 16 site. It was assumed that one of these two candidates would be chosen for the Apollo 16 sireand that the Apollo 17 site would be chosen from another candidate list. The Apollo 17 candidate sites under consideration at that time are discussed, in priority Order, in the following paragraphs. Tyeho and Davy Crater Chain No relative priority was established for Tycho and the Davy Crater chain. The objectives of a Tycho mission emphasized the southern highlands samples and impact phenomena. A mission to the Davy Crater chain had the same general objectives as an Alphonsus mission, namely the sampling of highlands, upland basin fill (Cayley Formation), and rocks of "deep-seated" origin. The site differs, however, in that (1) the Cayley is not modified by rilles and other volcanic features peculiar to Alphonsus, (2) the putative deep-seated material would be sampled at a crater chain instead of at ' a dark-halo crater, and (3) the highlands region (presumably pre-lmbrian) was not considered a_'apt to be mantled by the Cayley "volcanic" material as that at Alphonsus. (At that time, there was no knowledge of the brecciated nature of the Cayley Formation as sampled at Descartes.) It was noted that adequate photographs of Davy did not exist and would have to be obtained on an Apollo 16 mission to Descartes. ." Southwest of Mare Crisium Highlands" and the "Central

No relative priority was established for a site southwest of Mare Crisium and the ,"central highlands." The Apollo 15 mission was scheduled to overfly an extensive highlands region southwest of 1-1

Administration, Wash-

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APOLLO 17 PRELIMINARY SCIENCE REPORT for the Apollo 17 mission. At the meeting, the ASSB recognized both Descartes and Alphonsus as good sites. Descartes was selected as the Apollo 16 site, mainly for two reasons. First, more was known about the operational aspects of a Descartes mission because, in contrast to the only recently considered Alphonsus, Descartes had been a high-priority candidate site since before the Apollo 12 mission. Second, the Descartes prime objectives (sampling the Cayley and Descartes Formations) were independent of Apollo 14 and 15 results whereas an Alphonsus mission had a common objective with the Apollo 15 mission of "old highlands" sampling. At the same meeting, the ASSB designated Alphonsus as the prime candidate site for the Apollo 17 mission. (Alternatively, Descartes would have been designated had it not been selected as the Apollo 16 site.) Alphonsus was designated partly because the scientific arguments that had made Alphonsus a prime candidate for the Apollo 16 site had convinced the ASSB of the validity of the Alphonsus objectives. More to the point, however, Alphonsus was known to be operationally acceptable whereas all other Apollo 17 candidate sites had actual or potential problems. First, Tycho was deleted from further consideration because of concern about the rough terrain surrounding the landing ellipse. Second, the central highlands and the Davy Crater chain were questionable because of the necessity to rely on Apollo 16 photographs (i.e., insufficient time to create operational maps, models, etc.). Third, Gassendi, although not fully analyzed, appeared to be dominated by rough terrain. Fourth, the Copernicus central peaks appeared to be losing scientific interest. Finally, one could not count on Apollo 15 successfully photographing a suitable site in the region southwest of Mare Ctisium; that is, a site that was operationally acceptable and at least of equal scientific interest as Alphonsus. This, then, was the situation until after the flight of Apollo 15, on which were obtained both excellent photographs of the highlands between Mare Crisium and Mare Serenitatis and good X-ray and gamma ray data for extensive regions along the groundtrack. The next task was to determine if suitable sites could be found in this region. POST-APOLLO 15 ACTI VITI ES

Mare Crisium. It was believed that results from Apollo 15 X-ray and gamma ray spectrometers would enable determination of whether gross chemical differences exist between the Crisium and HadleyApenninus regions. An affirmative answer would increase the priority of the Crisiumareas. The central highlands between Descartes and Alphonsus were considered because they are expected to contain pre-Imbrian materials. As was true for Davy, a prerequisite to selection was acquisition of good photographs of the region on the Apollo 16 mission. It was recognized that a potential problem existed in using Apollo 16 photographs of either Davy or the central highlands for an Apollo 17 mission, but it was believed that the increased interval between flights, changed from 6 to 9 months, would make the turnaround possible, Gassendi A flight to Gassendi was viewed as a central-peaks mission with Copernicus-type objectives of sampling highlands materials (of impact-rebound origin) and of investigating impact phenomena. A mission to Gassendi had the additional objective of investigation of the crater floor, which exhibits features interpreted to result from isostatic rebound; also, the site is distant from Mare Imbrium. Copernicus Central Peaks

The Copernicus central-peaks site, previously of high priority, was greatly reduced in priority for the Apollo 17 mission (as it had been for the Apollo 16 mission) because Copernicus ray material had probably been sampled on the Apollo 12 mission and because there were already three sites (Apollo 12, 14, and 15) in the circum-Imbtium region of the Moon. A far-side site-most notably in Tsiolkovsky-was also briefly considered. Although it was shown to be possible, at first look, to support the mission by using a communications relay satellite beyond the Moon, it was believed that the time schedule for the mission preparation was too short and that the probability of a successful mission was less than that for a conventional near-side site. APOLLO 16 SITE SELECTION MEETING

On June 3, 1971, the ASSB met to select the Apollo 16 site and to designate a prime candidate site

The preliminary Apollo 15 gamma ray and X-ray spectrometer results indicated that the highlands region southwest of Mare Crisium is generally low in

APOLLO 17 SITE SELECTION radioactivity andhas a highaluminum-to-siliconratio, both thought to indicate an anorthositic highlands crust different from that of the Montes Apenninus region. Screening of the Apollo 15 photographs occurred during October 1971. Six highlandscontaining candidate sites, spread between Mare Crisium and Mare Serenitatis, were selected. Four of those sites were subsequently eliminated for operational reasons (too far east to allow sufficient tracking time between acquisition of signal and powered descent initiation). The two remaining were a "pure" highland site, designated "southwest of Crisium," and a combination highland-volcanic site on the southeastern edge of Mare Serenitatis, designated Taurus-Littrow. (For a detailed discussion of the site characteristics, see sec. 6 of this report.) When the two new sites were added to the still-viable high-priority candidates from the previous site selection discussion, a total of five Apollo 17 candidate sites emerged. In alphabetical order, they were Alphonsus, Copernicus central pea1_, Gassendi central peaks, southwest of Crisium, and TaurusLittrow. In December 1971, a Site Evaluation Document was sent to 32 lunar scientists, mo:_t of whom were either principal investigators for the Apollo 17 experiments or had been intimately involved in lunar studies and site selection discussions. The document included a presentation of the general scientific objectives for the Apollo 17 mission and a discussion of the particular attributes of the five previously mentioned sites. Recipients of the document were requested, first, to respond with their personal scientific priorities for the Apollo 17 mission and, second, to indicate how each candidate site might fulfill all the established objectives. They were cantioned against unrealistically adding new sites, were told that there could be no dependence on Apollo 16 photographs (the constraint which eliminated Davy Crater chain and the central highlandsascandidates), and were further presented with the following strong caveats concerning two of the candidates, 1. The highland site southwest of Cristum is in the highland terrain unit accessible to a Russian unmanned sample return spacecraft. (Luna 20 subsequently landed in that region.) Additionally, the site is relatively homogeneous and thus would not make efficient use of the Apollo sampling system, 2. Most lunar scientists believe that samples from Copernicus were obtained in ray material acquired on the Apollo 12 mission, The responses to the Site Evaluation Document

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were considered by an Ad Hoc Site Evaluation Committee in January 1972. A clear consensus among respondees and the Ad Hoe Site Evaluation Committee was apparent in terms of the following objectives for the Apollo 17 mission (in priority order). Each objective is discussed in more detail below. 1. Sampling pre-Imbrian highlands as far from the Imbrium Basin as possible 2. Sampling "young volcanics" 3. Orbital coverage 4. Traverse geophysics 5. Apollo lunar surface experiments package (ALSEP) (high priority for the heat flow experiment) Pre-I mbrian Highlands

Samples acquired to date had been dominated by mare materials. Relatively much was known about mare composition and formation but, even considering the Fra Mauro and Hadley-Apenninus samples, relatively little was known about the highlands, which constitute approximately 85 percent of the Moon. Earth-based photogeologic mapping, Apollo 14 and 15 sample results, and Apollo 15 orbital data all indicated that the highlands are complex and heterogeneous. These factors led to the desire to sample highlands further, but as far away as possible from the Imbrium Basin (the source of Apollo 14 and 15 samples and possibly some Apollo 12 samples).

Young Volcanics The limited lunar isotopic chronology developed to the time of committee discussion indicated that major lunar thermal and chemical evolution may have effectively ceased approximately 3 billion years ago. It was thought to be important to determine whether or not that theory is indeed true because the developing models of lunar origin and evolution were very sensitive to that assumption. The existence of lunar materials younger than 3 billion years was predicated on the evidence of superposition and relative crater densities. The putative "young" materials are generally dark and often associated with cone-type structures or dark-halo craters thought to be indicative of explosive volcanism. The explosive nature itself was judged significant for two reasons. 1. Explosive volcanism may indicate a relatively high content of volatlles in the erupting magmas; such volatlles were lacking in samples thus far seen.

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APOLLO 17 PRELIMINARY SCIENCE REPORT site selection resulted mainly from the absence of the network-type experiments of previous missions (e.g., passive seismometer, magnetometer, and laser ranging retroreflector). AD HOC SITE EVALUATION COMMITTEE DELIBERATIONS The candidate sites Copernicus and southwest of Crisium generated no enthusiasm among respondees to the Site Evaluation Document or among committee members for the reasons noted previously. All three remaining sites (Alphonsus, Gassendi, and Taurus-Littrow) contain highlands material, but the Ad Hoc Site Evaluation Committee saw no obvious way to discriminate among the highlands of the sites regarding either age or composition. Gassendi fulf'dled the objective Of being farthest from the edge of the • Imbrium Basin (approximately 1000 km), but the neares L Taurus-Littrowl 'was approximately 800 km distant. The difference of approximately 200 km was not deemed significant/A question remained about whether the crater wall of Alphonsus, the expected source of highlands samples, is mantled by Cayley volcanics. Conversely, the highland blocks at TaurusLittrow and the central peaks of Gassendi both appeared to contain "clean" exposures. Between Gassendi and Taurus-Littrow, an argument favoring Gassendi was made in that there had been no central-peak-type mission in the Apollo Program whereas Taurus-Littrow was a ring-basin near-side site similar to Hadiey-Apenninus. Young volcanics are not in evidence at Gassendi, and a strong argument could not be made regarding the relative value of the dark-halo craters at Alphonsus to the dark mantling blanket at Taurus-Littrow. Both regions were hypothesized to contain possible xenollths or laves (or both) from deep interior regions. The orbital science coverage arguments were not compelling. It was recognized that a Gassendi mission would result in the least duplication of Apollo 15 and 16 photography and would have the positive attribute of flying over the Orientale Basin in sunlight. However, more weight was given to the argument that the infrared radiometer and the lunar sounder could benefit more by the Taurus-Littrow groundtracks because of the greater variety of overflown targets. The Ad Hoc Site Evaluation Committee concluded that the Taurus-Littrow site was the best candidate,

Orbital science coverage was discussed from two aspects. On the one hand, there was a desire to maximize the amotlht of new photography, which meant favoring sites the orbital groundtracks of which least duplicated those of Apollo 15 and 16. On the other hand, it was argued that some of the new orbital experiments on Apollo 17 (infrared radiometer and lunar sounder) would benefit most by groundtracks covering both the iargest variety of features and the largest area (high-latitude sites), There was thought to be additional merit in flying the infrared radiometer and the lunar sounder over regions already covered by the Apollo 15 or 16 X-ray and gamma ray sensors and over a number of the circular mascon basins, Traverse Geophysics

The Apollo 17 mission was scheduled to include three traverse geophysics experiments: lunar seismic profiling, surface electrical properties, and luna i traverse gravimeter. Because all these experir_entS were designed, basically, to detect, layering, sites with a high probability of having layering were preferred by the respective principal investigators. The unanimous opinion of the Ad Hoc Site Evaluation Committee, however, was that tee traverse geophysics should not be a determining factor in the site selection; rather, it was reasoned that after the site was selected for other factors, one should determine how best to use the traverse experiment s. Lunar Surface Experiments Package ¢: A desire was expressed to emplace the heat flow experiment in a region significantly different from that of Apollo 15 (the only other heat flow location) or of the planned Apollo 16 site and to avoid local topography of a scale affecting the measurement, Opinion was also expressed that, given a choice, the mass spectrometer should be placed at a site that showed a history of transient events or "recent" volcanism. It should be noted that the decreased priority of ALSEP-related factors in the Apollo 17 Apollo

APOLLO 17 SITE SELECTION followed by Gassendi, with Alphonsus a weak third. The overall result was based primarily on the fact that, in terms of sample acquisition, Taurus-Littrow was a two-objective site (highlands, young volcanics) whereas Gassendi was a single-objective site (centralpeak highlands). The better orbital photography coverage for a Gassendi mission was not deemed equivalent to obtaining a second prime sampling objective. Alphonsus, also a dual-objective site, did not measure up to Taurus-Littrow primarily because of the uncertainty concerning Cayley mantling of the Alphonsus crater wall and the superior othital science for Taurus-Littrow groundtracks. The ranking (leveloped by the Ad Hoe Site Evaluation Corrtmittee, and presented to the ASSB, was consistent with that obtained by summarizing the 32 responses to the Site Evaluation Document. APOLLO 17 SITE SELECTION MEETING

1-5

The ASSB met on February 11, 1972, to select the Apollo 17 site. The scientific arguments and recommendations discussed in the previous subsection were presented, followed by a presentation of the operational considerations, of which only seiiected highlights are discussed in this report, Of the three candidate sites analyzed in detail, Gassendi presented the most problems. Although the terrain along the landing approach was acceptable, the landing area itself presented problems. Outside the nominal 3o landing ellipse, which was acceptably smooth, the terrain is heavily cratered, rolling, or contains rilles. If the lunar module were to land down range of the nominal ellipse, it was likely that, even if the landing were successful, the crewmen would not be able to traverse to the prime objective (the central peaks), particularly if there were a failure of the lunar roving vehicle (LRV). These problems were deemed sufficient that the NASA Lyndon B. Johnson Space Center (JSC) considered Gassendi unacceptable as an Apollo 17 site. At Alphonsus, both the approach terrain and the landing area were judged "highly acceptable," which was the status when Alphonsus was being considered for the Apollo 16 site. It was also determined that in the contingency situation of a walking mission (LRV failure), the crewmen could reach both the crater wall and the dark-halo crater material.

Although early analysis of the Taurus-Littrow site, performed just after the screening of the Apollo 15 photographs, had indicated that no serious problems were associated with the site, detailed plotting of the landing ellipse in the valley showed that with a 90 ° azimuth for the approach path and with a constraint to avoid the sudden rise in topography caused by the scarp, the fit of the ellipse in the valley became very tight. Because of the increased precision available from the Apollo 15 metric camera, however, it was shown that even without command module landmark tracking, the ellipse could be placed such that no landing problem would be caused by topography. (The westernmost part of the ellipse did include a small portion of the landslide, but it was well within the capability of the crew to redesignate out of that area should they be heading toward it.) In addition, as in the case of Alphonsus, it was determined that the prime objective at Taurus-Littrow was achievable on a walking mission (LRV failure), even if the landing were made outside the nominal ellipse. The ASSB accepted the JSC evaluation that Gassendi was operationally unacceptable and then focused on Alphonsus and Taurus-Littrow. It was first noted that, although both Alphonsus and Tanrus-Littrow were operationally acceptable, Alphonsus presented fewer risks. The risks were not related to safety but to mission success. The differences in probability of success were not quantifiable; that is, shades of gray rather than blacks and whites were involved. Because there were no strong operational discriminators, the discussion returned to the scientific attributes of the sites. A recapitulation showed that the scientific evaluation clearly favored TaurusLittrow over Alphonsus; the decisive factors were the certainty of acquiring highlands material at TaurusLittrow (remembering the possible mantling by Cayley materials of the highlands at Alphonsus), the superior orbital coverage, and the better use of LRV capabilities. The ASSB unanimously accepted that evaluation and recommended to the Associate Administrator for Manned Space Flight that TaurusLittrow be the Apollo 17 landing site. R E F E R E NC E 1-1. Hinners, N. W.: Apollo 16 Site Selection. See. 1 of the Apollo 16 Preliminary Science Report. NASA SP-315, 1972.

2. Mission

Description

Richard R. Baldwin a

The highly successful Apollo 17 manned lunar landing mission was the final in a series of three J-type missions planned for the Apotto Program. These J-type missions have been characterized by extended hardware capability, by a scientific payload larger than on the previous G- and H-series missions, and by the use of a battery-powered lunar roving vehicle (LRV). As a result of these additions, the Apollo 17 mission had a duration of 12.6 days, a time on the lunar surface of 75 hr with a total surface traverse distance of approximately 35 km, and a scientific instrument module (SIM) containing equipment for orbital experiments and photographic tasks. During their 22.1 hr of lunar surface extravehicular activity (EVA), crewmen collected approximately 110 kg of samples and took more than 2100 photographs. All Apollo landing missions are compared in figure 2-1 in terms of the science payload weight delivered to the lunar surface, the EVA duration, the surface distance traversed, and the weight of returned lunar samples. The landing site for Apollo 17 is on the southeastern rim of Mare Serenitatis in a clark deposit between massif units of the southwestern Montes Taurus, as shown in figure 2-2. These massif units (which are believed to be breccias from large basin ejecta), the dark mantle material, and a possible debris flow 5 km southwest of the landing site are features of major geological interest in the TaurusLittrow region. Scientific objectives of the Apollo 17 mission included geological surveying and sampling of materials and surface features in a preselected area of the Taurus-Littrow region, deploying and activating surface experiments, and conducting inflight experiments and photographic tasks during lunar orbit and transearth coast (TEC). These objectives were sarisfled on Apollo 17 by performance of scheduled aNASALyndon B. Johnson Space Center. 2-1

command module pilot (CMP)) was launched from the NASA John F. Kennedy Space Center at 11:33:00 p.m.e.s.t, on December 6, 1972 (05:33:00 G.m.t. on December 7, 1972). The command and service module (CSM), the lunar module (LM), and the SIVB later into mi. After CSM, LM, translunar booster stage were inserted 11 min 53 sec an Earth parking orbit of 91.2 by 92.5 n. two revolutions, at 08:45:37 G.m.t., the and SIVB spent stage were inserted into coast. G.m.t. on December 7, the CSM was

At 09:15:29

MISSION DESCRIPTION

2-3

FIGURE 2-2.-Landing site of Apollo lunar landing missions. Apollo 11 Ianded in Mare Tranquillitatis on July 20, 1969; Apollo 12 in Oceanus Procellarum on November 19, 1969; Apollo 14 in the Fra Mauro highlands on January 31, 1971; Apollo 15 in the Hadley-Apennines region on July 30, 1971; Apollo 16 in the Descartes region on April 21, 1972; and Apollo 17 in a valley at Taurus-Littrow on December 11, 1972. separated from the SIVB. Approximately 15 min la|er, the CSM docked with the LM. After CSM/LM extraction from the SIVB, the SIVB was targeted for lunar impact, which occulred on December 10 at 20:32:43 G.m.t. The impact location was approximately 84 n. mi. northwest of the phmned target point, and the event was recorded by the passive seismic experiments deployed on the Apollo 12, 14, 15, and 16 missions. Only one of the four planned midcourse corrections was required during translunar coast. A midcomse colrection (MCC) made at 17:03:00 G.m.t. on December 8 was a 1.6-sec service propulsion system burn resulting in a 10.5-ft/sec velocity change. The

2-4

APOLLO 17 PRELIMINARY SCIENCE REPORT completed with deployment of the LACE and the LSP experiment (except for explosive charges). Total ALSEP deployment, with relative locations of the experiments, is shown in figure 2-3. The deep core sample was taken concurrently with ALSEP deployment. Although difficulty was experienced in extraction, all three core sections were obtained. The neutron flux probe was then deployed to full depth in the deep core hole. Both the receiver and transmitrer of the SEP experiment were deployed as planned, with initial instrument operation scheduled during EVA-2. During ALSEP deployment, extra time was required to level the central station and the antenna gimbal. The resulting time-line deficit was compensated for by relocating the first traverse station to an area near the rim of Steno Crater. At station 1A, the crew collected geological samples, including a rake sample, and took a traverse gravimeter reading. A total of six gravity measurements and one gravimeter bias measurement were taken during EVA-1. At station 1A, the crew also deployed a 1-1b explosive package for the LSP instrument. During their return to the LM, the crew deployed a ½-1b explosive package. The first ALSEP data were recorded at 02:54:00 G.m.t. on December 12. The first EVA, which was 7 hr 12 min long, was completed at 07:06:42 G.m.t. on December 12.

first of two 40-min heat flow and convection demonstrations was begun at 00:33:00 G.m.t. on December 9. The second demonstration was begun 2 hr 20 min later. The SIM bay door was jettisoned at 15:05:40 G.m.t. on December 10. Lunar orbit insertion, executed at 19:47:23 G.m.t. on December 10, placed the spacecraft into a lunar orbit of 170.0 by 52.6 n. mi. Approximately 4 hr 20 min later, the orbit was reduced to 59 by 15 n. mi. The spacecraft remained in this low orbit for more than 18 hr, during which time the CSM/LM undocking and separation were performed. The CSM circularization maneuver, which was performed at 18:50:29 G.m.t. on December 11, placed the CSM into a 70.3by 54.3-n. mi. orbit, At 14:35:00 G.m.t. on December 11, the CDR and the LMP entered the LM to prepare for descent to the lunar surface. The LM was powered up and all systems were nominal. A maneuver at 18:55:42 G.m.t. on December 11 placed the LM in an orbit with a perilune altitude of 6.2 n. mi. Approximately 47 min later, the powered descent to the surface began, LUNAR SURFACE ACTIVITIES

Following a nominal descent sequence, the spacecraft landed at 19:54:57 G.m.t. on December 11 in a valley at Taurus-Littrow, less than 200 m from the preferred landing point. The best estimate of the lunar surface landing position is latitude 20c10 ' N and longitude 30°46 ' E (ref. 2-1). The Apollo 17 landing site in relation to those of all previous lunar landing missions is shown in figure 2-2. The first lunar surface EVA began at 23:54:49 G.m.t. on December 11, with the CDR egressing at 00:01:00 G.m.t. on December 12. Television coverage began after installation of the ground-commanded television camera and the high-gain antenna on the LRV. The first television pictures were received at 01:10:49 G.m.t. Before leaving the LM for the ALSEP site, the crew deployed the cosmic ray experiment. The site selected for the ALSEP was approximately 185 m west-northwest of the LM. Deployment of the heat flow experiment was nominal, with both probes inserted to a depth of 2.54 m. The LEAM experiment and the LSG were also deployed nominally. Preliminary operations with the gravimeter did not indicate the beam-nulling problem that was later encountered. The ALSEP group was

;,-'" ge0ph0ne i "" Geophone Ge0ph0ne 1 RTG

: D:rill'_ Ge0ph0ne casings 2 - and

LACE

"x

N

FIGURE 2-3.-Deployment of the Apollo 17 ALSEP, showing the relative locations of the central station, radioisotope thermoelectric generator (RTG), and the five experiments.

MISSION DESCRIPTION The second EVA was begun at 23:28:06 G.m.t. on December 12. The second major sampling stop of the mission was made early in EVA-2 at Nansen Crater, where the crew sampled primarily the rock debris at the base of the South Massif. After leaving Nansen Crater, the crew made an unscheduled stop (station 2A) to check the gravity gradient between the South Massif and the valley. The major geological objective of the third sampling site near Lara Crater was the scarp that runs north-south between the massif units, Activities at this stop included an exploratory trench and a core sample, which was stored in the core sample vacuum container. Traverse station 4 was at Shorty Crater, a 110-m dark-halo crater. Sampling at this location was focused on deposits and rocks at the crater rim. A trench dug in the crater rim exposed the much-discussed orange soft. A double core sample was also obtained at station 4. Blocks of subfloor basalt were found at Camelot Crater (station 5), and sampling included a search for dark mantle material. During the traverse on EVA-2, the SEP experiment was operated and the crew deployed l/8-, 6-, and 1/4-1b explosive charges. Seven traverse gravimeter measurements were taken: one each at stations 2, 3, 4, and 5; one between stations 2 and 3; and two at the LM site. Finally, eight LRV sampling stops were made at points intermediate to the major stops to increase the areal density of geological sampling sites. During the second EVA, it was discovered that the sensor beam of the LSG could not be nulled, even though the LMP reverified that the instrument was level and the gimbal was free. The second EVA was 7 hr 37 min long and ended at 07:05:02 G.m.t. on December 13. The third EVA began at 22:25:48 G.m.t. on December 13. The cosmic ray detector was recovered early in the EVA to avoid exposure to an excess of low-energy solar protons. The first two traverse stops (stations 6 and 7) of EVA-3 were made at the base of the North Massif. Geological activities in these areas emphasized boulders and boulder tracks and included the dark mantle material and the massif/valley interface. A rake sample and a single core sample were obtained at station 6, and several rock chips were collected from a 3-m boulder at station 7. At station 8 (Sculptured Hills), samples included the dark mantle plains material. The crew obtained a trench sample and a rake sample at this location as part of the sampling plan to look for differences between the Sculptured Hills and the Massifs. Sampling at station

2-5

9 (Van Serg Crater) was concentrated on the crest of the crater rim and the ejecta blanket southeastward of the rim, at both of which were found soft, dark-matrix breccias. A f'mal trench sample and double core were obtained at this station. Station 10 was deleted to obtain additional closeout time for completion of ALSEP photography and for further attempts to resolve the gravimeter problem. During EVA-3, four LRV sampling stops were made and traverse gravimeter measurements were taken at stations 6, 8, and 9 and at the LM. The remaining two explosive packages for the LSP experimerit were also deployed. Late in EVA-3, the LMP made a last, unsuccessful attempt to null the sensor beam of the LSG. One of the f'mal science activities in the EVA was retrieval of the neutron flux probe from the deep drill core hole. The third EVA ended at 05:40:56 G.m.t. on December 14. The LM ascent stage lifted off the Moon at 22:54:37 G.m.t. on December 14. Lift-off and ascent were recorded by the ground-commanded television assembly on the LRV. After a vernier adjustment maneuver, the ascent stage was inserted into a 48.5by 9.4-n. mi. orbit. The LM terminal phase initiation burn was made at 23:48:58 G.m.t. on December 14. This 3.2-sec maneuver raised the ascent stage orbit to 64.7 by 48.5 n. mi. The CSM and the LM docked at 01:10:15 G.m.t. When the LM ascent stage was jettisoned at 04:51:31 G.m.t. on December 15, the separation velocity was low, necessitating an evasive 2-ft/sec maneuver by the CSM. Deorbit ruing of the ascent stage was initiated at 06:31:14 G.m.t. on December 15. Impact occurred 19 rain 7 sec later approximately 0.7 n. mi. from the planned target at latitude 19°56t N and longitude 30°32' E_ The ascent stage impact was recorded by the four Apollo 17 geophones and by each ALSEP at the Apollo 12, 14, 15, and 16 landing sites. I N F L I G H T E X P E IqIM E NTS A N D P H OTOG RAP H IC TAS KS Experiments and photographic tasks were performed in lunar orbit and during both the translunar and transearth coast phases of Apollo 17. Equipment needed for performance of CM photographic tasks, visual observations of the Moon, the visual light flash phenomenon, the Nal scintillation crystal experiment, and the heat flow and convection demonstration were stowed in the CM. Equipment for other

ments and photographic tasks are shown in figure 2-5. The envelope of suborbital tracks for the lunar orbital camera, and Operational laser altimeter. The for inflight experiequipment. periods S-band transponder Inflight science activities on Apollo 17 were phase of the mission is shown in figure 2-6. conducted over a period of approximately 220 hr,

iiil)ilt t synlhet'tc aperture radar

Tii film cassette _L._..-Removable

' / FarUV spectrometer'

_ ___ _

_ "',,,_',: ,

!_ _ --_ Lunar sounder optical recorder with film cassette

G.m.t., December 10, and terminating approximately 3 hr before splashdown. During this interval, the following science activities were conducted; photography of most of the lunar surface area overflown in sunlight; active electromagnetic sounding of the hmar surface and subsurface over portions of the near side and the far side of the Moon; passive sounding tion of electromagnetic interference for determinaand cosmic

IR scanning radiometer FIGURE 2-4.-Scientific equipment, including orbital experiment instruments and photographic equipment, located in the SIM bay of the service module,

noise; thermal mapping of more than one-third of the lunar surface; investigation of lunar atmospheric

MISSION DESCRIPTION composition by UV spectral measurements; determination of gross lunar topography along groundtracks; free-flight measurements of spacecraft velocity for determination of lunar gravity anomalies; visual geological surveys of selected lunar regions in sunlight; and observation of solar atmospheric, galactic, and extragalactic sources of far UV radiation, Ten hr 31 sec of active lunar sounder data were recorded on film, including two consecutive revoluLions each in the HF and VHF ranges, as well as specific targets in each of these ranges. The sounder was operated in the receive-only mode on both the hmar near side and far side. Near the landing site, receive-only data were obtained by the sounder, both with and without the SEP transmitter operating. The sounder was operated for 24 hr during transearth coast to help determine levels of terrestrial noise. Problems were encountered with the extension and retraction of the HF antennas. A faulty talkback indicator and low temperature of the extension/ retraction mechanism were blamed for these operational delays, which caused no loss of data. Infrared scanning radiometer data were obtained
Re_luti0n Missionevent 36 37 38 3g to1 41 42 a3 44 45 46 4? 48 49

2-7

for 100 hr in lunar orbit and 10.5 hr in transearth coast. A total of 108 radiometer measurements were made during orbital operation, covering one-third of the lunar surface. Far UV spectral data were collected for a total of 80 hr hi lunar orbit and approximately 60 hr during transearth coast. Experiment operation included a solar atmospheric observation added in real time. High-quality S-band transponder data were obtained over Mare Serenitatis, Mare Crisium, and the Taurus-Littrow site. The data were taken in lowaltitude orbits and will help confirm results obtained from the Apollo 15 mission. The Apollo window meteoroid and the gamma ray crystal experiments were passive and required no crew activities. The CM window has been retrieved. Activation measurements on the gamma ray crystal were begun 1.5 hr after spacecraft entry, and early indications are that information return from the experiment is more than was expected. Panoramic camera photography was obtained on portions of eight lunar orbit revolutions and after transearth injection. A five-frame sequence was ob50 51 5g 53 54 55 56 57 _eUis0n ,,c_1" _ m m _lkLM impact m _ Iii • I m i _ i i mm 61 62 63 61 65 66 67 68 12

FIGURE 2-6.-Lunar surface groundtrack envelope of the Apollo 17 orbiting spacecraft for revolutions 1 to 75. Areas of additional data coverage outside the envelope are determined by the fields of view of experiment instruments and photographic cameras. (a) Near side.

rained on revolution 36 with the camera axis inclined
40 ° to the south of the groundtrack. On the third sequence of photography during the 15th revolution, an erratic velocity-to-height (V/h) signal was noted; the remainder of panoramic photography was performed with the camera V/h setting in the manual override position. During the final lunar orbit operation of the camera, the stereographic drive motor

failed, causing the final 8 min of photography to be
obtained in the monographic rather than the planned stereographic mode. Vertical mapping camera photography was obtained on 12 revolutions and after transearth injection. For the second mapping photography sequence, the camera deployment time was longer than expected. To avoid possible failure of the deployment

MISSION

DESCRIPTION

2-9

80° 70 °

Northpole

80 ° 70 ° 60° 50 °

50 °

400

40*

20 °

20 °

10 °

0o

0°

10'

10 °

30°

O°

40 °

LO°

50° 600 70 = 80° South pole 80° 70° 60 °

FIGURE 2-6.-(b) Far side.

mechanism, the camera was left deployed between several photographic passes. On revolution 49, the camera was operated from the retracted position, thus losing stellar camera coverage on this sequence. The laser altimeter operated well throughout the mission, obtaining 3769 ranging measurements. A 30-min altimeter sequence scheduled for revolution 62 was deleted to allow a special attitude sequence for the far UV spectrometer. During the final sleep

period in lunar orbit, the altimeter was operated to obtain 10 hr of continuous data, in addition to the planned coverage. Photographic and visual observations from the CM were made as scheduled, with the exception of the second of two solar corona sequences, which was omitted because of time-line and attitude constraints. The zodiacal light was photographed three different times: once each in red light, blue light, and

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APOLLO 17 PRELIMINARY SCIENCE REPORT Tile CMP performed an inflight EVA at 20:27:40 G.m.t. on December 17 during transearth coast. The EVA lasted for approximately 1 hr 7 rain, during which time the CMP retrieved the lunar sounder film and the panoramic and mapping camera film cassettes.

plane-polarized white light. Photographs of the hmar surface from the CM included 10 color strips, eight black-and-white sequences near the terminator, and additional photographs to document visual observations. Formally scheduled visual observations of 10 lunar surface targets were made by the crew using 10-power binoculars. Accompanying comments by the crew were made and recorded for subsequent use. The biostack II and BIOCORE experiments were passive and required no crew activities. The experiments were recovered after completion of the mission.

The first phase of man's active exploration of the Moon came to an end with the Apollo 17 mission. Many questions about lunar science have been answered during the intensive activity of the last decade, but many more remain to be answered. Some of the unanswered questions will be answered in the future from data already returned but as yet not fully analyzed, and some will have to wait for data yet to be returned from instruments already in place on the lunar surface. Still other questions must await further exploration, The basic objective of the Apollo 17 mission was to sample basin-rim highland material and adjacent mare material and investigate the geological evolutionary relationship between these two major units, In addition to achieving this general geological objectire, it has also been possible to measure directly the thermal neutron flux in the regolith_ to explore geophysically the subsurface structure of the valley floor, to determine the constituents of the lunar atmosphere and observe their variations during the lunar day and night, and to explore even more of the lunar surface remotely from orbit, These initial results and others will someday be combined into a coherent picture of the evolution of the Moon that will reflect more light on both the abstract and specific problems of the evolution and current conditions of the Earth and other planets, That will be the true legacy of the Apollo Programnot just the sometimes apparently fragmented preliminary results seen here. LUNAR FIE LD GEOLOGY

light mantle, the dark mantle, the subfloor, the Sculptured Hills, and the massifs. The light mantle unit was sampled at stations 2, 2A, and 3 and at two lunar roving vehicle (LRV) sampling stops. Preliminary indications from these samples are that the light mantle is primarily finegrained debris that includes cataclasites and breccias similar to those attributed to the South Massif and different from the regolith elsewhere on the valley floor. These observations are in agreement with the hypothesis that the light mantle unit resulted from a slide down the northern face of the South Massif that occurred approximately 10 8 yr ago as indicated by crater counts. The slide perhaps was caused by the impact of some secondary ejecta at the top of the South Massif. The dark mantle unit remains one of the enigmas of the Apollo 17 mission. Photogeological observations of the subdued appearance of the larger craters and the general paucity of craters on the valley floor had led to the expectation of a "mantling" unit which covered the valley floor sometime after most of the regolith formation had taken place and which was perhaps Copernican in age. Because of dark areas in depressions in the surrounding highlands, the mantling unit was expected to have also covered at least part of the highlands. No such unit has so far been detected in situ. Instead, everywhere on the Valley floor except in the area of the light mantle, the soil appears to be regolith largely derived from the underlying subfloor basalt unit. A possible dark mantle component in the regolith is the dark glass sphere unit of unknown origin but possibly related to the orange glass of station 4. The age of the dark glass, however, is 3.7 X 10 9 yr, and it is apparently well mixed into the regolith, which seems to rule it out as the mantling unit. The subfloor unit was well sampled at a number of stations (the Apollo lunar surface experiments package (ALSEP) site and stations 1A, 4, 5, and 9?) and 3-1

Premission photogeology of the Taurus-Littrow valley and its environs led to the expectation of sampling five different major stratigraphic units: the

aNASALyndon B. Johnson SpaceCenter.

3-2

APOLLO 17 PRELIMINARY SCIENCE REPORT is composed of breccias that probably were produced by one or more basin-forming events. An event of great interest during the geological exploration of the valley of Taurus-Littrow was the discovery of deposits of orange glass on the rim of Shorty Crater. Present indications are that the orange glass is fairly old (3.7 × 10 9 yr); that shortly after its formation, it was well buried; and that only recently (20 to 30 X 10 6 yr ago), it was excavated by the Shorty Crater impact. Some traces of the orange glass spheres exist in the regolith elsewhere in the valley. The general premission model of a graben valley that was formed as part of the Serenitatis event, perhaps reactivated since then, and later partly filled with a basalt flow (or flows) during the episode of mare f'flling is corroborated and more tightly defined by the data analyzed to date. PRELIMINARY SAMPLE

was shown to be a 3.8 × 109-yr-old, massive, lightcolored mare basalt unit containing 10 to 15 percent vesicles, 30 to 40 percent plagioclase, together with clinopyroxene and ilmenite as rock-forming plagioclase. Some local variations in texture, mineralogy, and chemistry exist. Geophysical experiments on the mission also indicate the existence of such a layer with a thickness of approximately 1 km. Samples of the subfloor basalt were primarily taken from boulder-size ejecta at large craters that penetrated the regolith to the underlying unit. Samples of the basalt were also obtained from the regolith that has been developed on top of it, notablyin a widespread series of LRV samples as well as at the major geological stations. Samples from station 9 in particular may be from deep in the regolith (but not quite to the depth of the basalt unit), The Sculptured Hills unit was investigated at station 8. Because of the lack of any identifiable material that has moved downslope, sampling of the Sculptured Hills unit consists of samples of the regolith from theIower part of the slope. Because the soil undoubtedly is composed of material from both the valley regolith and the Sculptured Hills regolith, identification of the Sculptured Hills rock types will have to be delayed until a comparison can be made between the valley regolith and the soft collected at station 8. At the moment, no more is known about the Sculptured Hills unit than that it is a highland unit morphologically different from the massifs and the reasons for this difference are unknown, The massif unit was sampled at three locations at the bases of the South and North Massifs (station 2 and stations 6 and 7, respectively) and also in the light mantle. Five different boulders (one of which, at station 6, had broken into five boulder-size pieces) as well as soils were sampled at the three stations. The boulders undoubtedly represent units in place higher up the massif slopes (in the upper half of the South Massif and the lower third of the North Massif). All the boulders are breccias of a moderately complex nature, similar to those from the Apollo 15 and 16 sites, and are indicative of more than one brecciation event. There is indication of a correlation of breccia types between the North and South Massifs, but definitive conclusions on this must wait for additional geochemical analyses and detailed petrologic examination. In the meantime, it can be concluded that the massif unit, probably raised by the Serenitatis event,

ANALYSIS The suite of rock samples returned from the Apollo 17 mission is a quite varied one. Included in the samples are basalts, dark-matrix breccias and agglutinates, green-gray breccias, bhie-gray breccias, light-gray breccias, brecciated gabbroic rocks, and others (including a dunite clast composed of more than 95 percent olivine). The basalts are quite uniform in composition and are generally similar to the Apollo 11 basalts. They are generally vesicular, have variable grain sizes as large as 2 mm, and consist of approximately 25 to 30 percent plagioclase. The basalts are high in titanium like the Apollo 11 basalts but are much lower in nickel. In detail, chemical differences within the Apollo 17 basalt suite argue for at least two different basalt types. The dark-matrix breccias and agglutinates are derived from the basalt regolith of the valley floor and contain clasts of basalt. The green-gray breccias are predominantly matrix with a small percentage of mostly mineral clasts. The matrix is coherent, is rich in poikilitic orthopyroxene, and has vesicles as large as several centimeters in diameter. The bhie-gray breccias are matrix breccias with a more varied population of clasts than the green-gray breccias. The blue-gray matrix is slightly vesicular with some fine-scale banding and a recrystallized texture. The light-gray breccias are layered and foliated, have a higher percentage of clasts, and are less coherent than

SUMMARY OF SCIENTIFIC RESULTS the green-gray and blue-gray types. The clasts, both lithic and mineral, are generally feldspar rich and include first- and second-order breccias. The lightgray matrix texture is fragmental. The brecciated gabbroic rocks are similar to the crushed cataclastic anorthosites returned on the Apollo 15 and 16 missions, The breccias can be divided chemically into two groups: the blue-gray, green-gray, and light-gray breccias with approximately 50 percent normative plagioclase and the brecciated gabbroic rocks with approximately 70 percent normative plagioclase. The blue-gray, green-gray, and light-gray breccias have strikingly more potassium, phosphorus, rubidium, yttrium, zirconium, and niobium than the brecciated gabbroic rocks. Based on analysis of one light-gray breccia, they appear to have slightly higher rubidium, yttrium, and zirconium contents and a slightly lower strontium and nickel content than the blue-gray and green-gray breccias. Both the major- and traceelement compositions of the blue-, gree:n-, and lightgray breccias are very similar to those of the KREEP-like rocks (those that are rich in potassium, rare-earth elements, and phosphorus) from Descartes and are especially similar to those of the brown-glassmatrix breccia from Hadley-Apennine. The brecciated gabbroic rocks chemically resemble similar rocks from the Apollo 16 mission and especially closely resemble Apollo 15 sample 15418. The Apollo 17 soils are generally divided into two types: soils on the valley floor derived as regolith from the underlying basalt and soils from the massifs and light mantle derived as regolith from the breccias, At the transition zones between the two units and at the foot of the Sculptured Hills, the soils are a mixture of the two types. Exotic glasses (orange and black glass spherules), first noticed at Shorty Crater, are present in soils throughout the valley. The orange soil is generally basaltic but has a higher percentage of magnesium and a very strikingly high abundance of zinc as well as other trace-element differences (e.g., high chromium oxide). The orange soil also contains more low-temperature volatiles than do other soil samples. SURFACE ELECTRICAL PROPERTIES EXPERIMENT

3-3

lunar regolith in situ and also to provide information on the subsurface structure in the region covered by the geology traverses. Electromagnetic radiation at six frequencies between 1 and 32 MHz was transmitted from a fixed crossed-dipole antenna and received through an antenna attached to the LRV. Preliminary indications are that useful data were received only during the traverse from the SEP site to station 2. On the basis of early analysis of the signals recorded during that traverse, two different models can be developed. One mode1 explains the observations in terms of a dielectric constant that increases as a function of depth, in particular with a marked discontinuity at a depth of approximately 50 m. The other model includes two layers having different dielectric constants the interface of which decreases in depth from approximately 20 m at the lunar module (LM) site to 15 m at station 2. LUNAR TRAVERSE GRAVIMETER

By the comparison of measurements made on the Earth and at the Apollo 17 landing site with the same instrument, the lunar traverse gravimeter, the value of gravity at the LM site was found to be 162 695 -+5 mgal. Relative gravity measurements were obtained for a network of 12 stations spread across the valley floor. At four stations near the LM (the LM, ALSEP, and SEP sites and station 1A), the 10 measurements agree within approximately + 3 regal. At four other stations on the valley floor located as far as 5 km from the LM (stations 3, 4, 5, and 9), the Bouguer anomaly is generally small and slightly negative (-5 to -10 regal). At four other stations either at or very near the massifs (stations 2, 2A, 6, and 8), the Bouguer anomaly increases rapidly to between -20 and -25 regal. Between stations 2A and 3, a distance of less than 1.5 kin, the Bouguer anomaly changes from -20 to -5 mgal. The Bougner anomaly curve has been interpreted in terms of a model with a 1-kin-thick plate of basalt for the valley floor, assuming a density contrast of 0.8 g/cm 3 with respect to the material on either side. LUNAR SEISMIC PROFILING EXPERIMENT

The surface electrical properties (SEP) experiment was used to measure the dielectric cortstant of the

The lunar seismic profiling experiment is an extension of the active seismic experiment carried on the Apollo 14 and 16 missions. Eight explosive

charges (ranging in size from 57 to 2722 g) were deployed at distances between 100 and 2700 m from a triangular geophone array. These charges were later detonated on command from the Earth, and traveltime measurements were obtained that, together with the LM-impact signals, indicate a three-layer model for the valley floor at Taurus-Littrow. The first 248-m-thick surface layer has a seismic velocity of 250 m/sec. The second layer, extending to a depth of approximately 1200 m, has a seismic velocity of 1200 m/sec. Below 1200 m, the third layer, with a seismic velocity of approximately 400 m/sec, begins. A reasonable model, with basalt flows f'dling the valley of Taurus-Littrow to a depth of 1.2 km, can be derived from these observations. The 4000-m/sec velocity for the third layer is a valuable tie point between the shallow surface velocities measured earlier and the deeper velocities measured by the passive seismometers from distant events, LUNAR SURFACE GRAVIMETER

ATMOSPHERIC COMPOSITION EXPE R IM ENT

The lunar atmospheric composition experiment is designed to identify the various gases in the lunar atmosphere and to determine the concentration of each species. Previous measurements using the cold cathode ion gages have been limited to total gas concentrations. Preliminary results for the first three lunations indicate the presence of (1) three native species in the lunar atmosphere (helium, neon, and argon) and (2) a large number of other species, some of which are undoubtedly contaminants (e.g., atomic hydrogen, nitrogen, oxygen, chlorine, hydrochloric acid, and carbon dioxide). The measured concentrations of these contaminants has continued to decline with the passage of time. The measured helium concentrations and their behavior as a function of phase in the lunation (increasing by a factor of 20 toward lunar midnight) are in agreement with predictions that helium does not freeze out on the surface at night and that its source is the solar wind. The concentration of neon, measured only at night, is a factor of 20 lower than predicted, and the results are not understood. The concentration of argon also decreases (in fact, becomes undetectable) during the night as expected for a gas that freezes out on the surface during the lunar night. Shortly before dawn, the argon concentration begins to rise, apparently indicative of the migration of argon across the approaching sunrise terminator (a predawn argon breeze); the behavior of the contaminants is markedly different in that they show a sharp rise just at local sunrise. HEAT FLOW EXPERIMENT

The lunar surface gravimeter was designed to make very accurate (1 part in 1011) measurements of the acceleration of lunar gravity and of its variation with time. These measurements should allow investigations of gravitational waves by using the Moon as an antenna and also investigations of tidal distortions of the shape of the Moon. Following deployment of the gravimeter, problems occurred in trying to balance the beam. These problems were probably caused by an incorrect mass of the beam and have at least partly been overcome by applying pressure on the beam with the mass-changing mechanism. Data in the form of seismic events at sunrise and sunset have been received, and it is hoped that the instrument can be used in its off-nominal mode to obtain the data for which it was designed. LUNAR EJECTA AND METEORITES EXPERIMENT

The objectives of the lunar ejecta and meteorites experiment, which is part of the ALSEP, are to detect secondary particles that have been ejected by meteorite impacts on the lunar surface and to detect primary micrometeorites themselves. The particle detectors of the instrument are multilayered arrays that are capable of measuring the velocity and energy of

The deployment of a second heat flow experiment on the lunar surface as a part of the Apollo 17 ALSEP allows comparison of lunar heat flow measured at two different stations, the Apollo 15 and 17 landing sites. Both Apollo 17 probes were successfully inserted to their full depth of 2.36 m. Preliminary results indicate that the heat flow at the Apollo 17 site is 2.8 × 10-6 W/cm 2 for the first probe and 2.5 × 10 -6 W/cm 2 for the second probe.

SUMMARY OF SCIENTIFIC RESULTS These values can be compared with a revised value for the Apollo 15 site of 3.1 X 10-6 W/cm 2. The uncertainty for all three values is +-20 percent. The heat flow gradient for probe 1 is uniform in agreement with a similar observation made at the Apollo 15 site. For probe 2, however, the gradient is definitely not uniform and the difference is believed to be due to insertion of the probe very near a buried boulder, Corrections for topography have not yet been applied to the heat flow values. Although the size of these corrections is not clear at this time, it would appear that they will result in a reduction of the present values by a factor of 15 to 25 percent for the Apollo 17 measurements and an uncertainty of +- 10 percent for the Apollo 15 measurements. The possible resulting difference between the heat flow values measured at the two different sites may be explainable in terms of higher thorium abundances, observed by the Apollo 15 gamma ray instrument, in southeastern Mare Imbrium as compared with southeastern Mare Serenitatis. In any case, values of the heat flow between 2.4 X 10-6 and 3.0 X 10 -6 W/cm 2 are confirmed as characteristic of more than one site of fire Moon. If applied generally to the entire Moon, those values argue for relatively large quantities of radioisotopes in the outer layers of the Moon. LUNAR NEUTRON PROBE EXP['RIMENT PASSIVE SEISMIC EXPERIMENT

3-5

A passive seismometer station was not included in the Apollo 17 ALSEP. The impacts of the Apollo 17 LM and SIVB were observed by the four stations already in place at distances as great as 1750 km. These impacts and the occurrence of other natural events since the Apollo 16 mission (especially an impact on the far side near Mare Moscoviense) have helped to further define the lunar seismic model below the "crust" as being characterized by a thick, seismically inactive, relatively homogeneous lithosphere that encloses an asthenospheric zone of partial melting. Moonquake activity appears to be concentrated at the boundary between these two zones at a depth of approximately 1000 km. Evidence has also been found for the existence of two belts of seismic activity as plotted by epicenter locations. Seismic observations to date cannot be used to either confirm or deny the possible existence of a small iron-rich core. COSMIC RAY EXPERIMENT A new set of cosmic ray detectors was carried to the surface of the Moon on the Apollo 17,mission. Two sets of detectors (including mica, quartz, glass, plastic, and foil) were exposed, one set facing the Sun and one set in the shade facing away from the Sun. During the time that the detectors were exposed, no significant solar activity occurred. Although the absolute flux levels for the 0.02- to l-MeV/amu energy range were considerably lower than those for the Apollo 16 mission, the shape of the spectrum is similar to that for the flare that occurred during the Apollo 16 mission and indicates that proportionate numbers of energetic particles are emitted by the Sun even during quiet periods. Heavy-element enrichment noted during flares is also present during the quiet periods. Tracks were also noted in the detectors facing away from the Sun. Because these particles also have a "solar energy" spectrum and presumably come from the Sun, the "antisolar" tracks indicate the existence of irregularities in the interplanetary magnetic field outside the orbit of the Earth that are capable of "reflecting" these solar cosmic rays. SOl k M ECHAN ICS EXPE R IMENT Although there is considerable local variability in the properties of the soil, large-scale averages have

Time-integrated fluxes of thermal neutrons (_< 1 eV) as a function of depth in the regolith were measured using the lunar neutron probe. These measurements were accomplished with targets of boron-10 and uranium-235 placed at intervals along a 2-m rod that was inserted into the hole left by the deep drill core when it was extracted. Preliminary analysis of tracks in the mica detectors that were used in conjunction with the uranium-235 targets agrees with both the magnitude and shape of previous theoretical work on the neutron flux as a function of depth in the lunar regolith. Therefore, the problem concerning the fact that integrated neutron dosages for soil samples indicate more rapid and/or deeper regolith turnover than geological evidence indicates is not resolved. Hence, neither the mixing depth nor the time scale of the regolith model, both of which are needed to fully interpret the gadolinium ratios, has been defined,

3-6

APOLLO 17 PRELIMINARY SCIENCE REPORT surface. This low value (at least 10 times lower than predicted for a transient lunar atmosphere resulting from the solar wind) implies that during diffusion at the lunar surface, hydrogen molecules are formed. The upper limits for hydrogen molecules from the current observations are not inconsistent with this idea. Xenon is also less abundant than predicted as a native constituent of the lunar atmosphere. INFRARED The infrared SCANNING RADIOMETER carried in the

been very similar for all Apollo landing sites with the exception of Descartes, where the relative density is notably lower than at the other sites. Although the soil density in the Apollo 17 double-core sample obtained from the orange soil is the highest yet found on an Apollo mission, the difficulty in driving the core tube was not exceptional, leading to the conclusion that it is not a low mean porosity but a high specific gravity of the individual grains that causes the observed high density. Because of the long-term stability of the deep drill hole, it is concluded that the soil strength is relatively high at depths on the order of 1 to 2 m.

scanning radiometer,

APOLLO

LUNAR

SOUNDER

EXPERIMENT carried in

The Apollo lunar sounder experiment

the scientific instrument module (SIM) bay was a three-frequency (5, 15, and 150 MHz) chirped radar sounder. Depth of subsurface exploration, in terms of features defined by changes in the dielectric constant, decreased with increasing frequency, The Apollo lunar sounder was designed for three primary modes of operation: sounding, profiling, and imaging. The sounding mode pertains to the detection and mapping of subsurface features such as a probable 100-m-deep interface detected in western Mare Serenitatis. The profiling and imaging modes, which are similar to conventional surface return radars, can provide quantitative metric and topographic data as welt as albedo measurements. Preliminary results obtained by processing some small selected portions of the data indicate that useful data were obtained, ULTRAVIOLET SPECTROMETER

SIM bay, was used to map the lunar surface in 352-km-wide strips centered on the groundtracks with a resolution of better than 10 km. This mapping was accomplished by sweeping the 1° instantaneous field of view in contiguous strips perpendicular to the orbital groundtrack. The spectral bandpass extended from 1.2 to 70/.tm. In addition to a number of individual thermal anomalies, preliminary examination of the data shows, among other things, a great concentration of nighttime thermal hot spots in the Oceanus Procellarum region, particularly in contrast to the relative smoothness of nighttime scans of highland areas. The nighttime thermal picture of the far side of the Moon is relatively featureless compared to that of the near side. S-BAN D TRANSPONDE R

The general similarities of the Apollo 15 and 17 groundtracks allowed good comparisons to be made between gravity data obtained on the two separate missions. Agreement in many areas (e.g., over Mare Crisium) was good. The model for the Serenitatis mascon, however, was shown to be inadequate; the Apollo 17 observations were 1.6 times larger than those predicted for the Apollo 17 groundtrack by the Apollo 15 model. Because the new Apollo 17 data increase the areal coverage of Mare Serenitatis, it is obvious that an improved model can be expected. Very good areal coverage was also obtained of Grimaldi Crater, and there is evidence that this mascon has the largest mass distribution yet observed for any mascon (approximately 1000 kg/cm2). An estimate derived from these observations for the value of lunar gravity at the landing site (162 722 regal) compares very well with that obtained by the lunar traverse gravimeter (162 695 mgal).

The ultraviolet spectrometer flown in the SIM bay of the Apollo 17 spacecraft was a single-channel scanner having a 12 ° by 20 ° field of view and covering a spectral range of 1180 to 1680 )_ (118 to 168 nm). The entire spectral range was repetitively scanned every 12 sec. The primary objective of the instrument was to measure the lunar atmosphere using resonance line scattering. No lunar atmospheric constituents were detected except for a short-lived (2 to 4 hr) "cloud" just after the descent of the LM. Among new lower limits that were established is one of _< 10 atoms/cm 3 for atomic hydrogen at the lunar

SUMMARY O'F SCIENTIFIC RESULTS BIOSTACK EXPERI MEN'F

3-7

Other organs are also being examined, but no results are yet available. VISUAL LIGHT PHENOMENON

The Apollo 17 biostack experiment (biostack II) was of very similar configuration to the Apollo 16 biostack experiment (biostack I). The total radiation dose received by biostack II was approximately 15 percent higher than that received by biostack I. The primary difference between the two experiments was the different set of species flown on the two missions, (Three of the four species flown on Apollo 16 were flown again on Apollo 17 as well as three other species.) Initial results, using organisms not hit by cosmic rays, show that, as on the Apollo 16 mission, viability is apparently not affected by other factors related to space flight. The Apollo 16 results showed markedly different sensitivity to radiation between different strains of the same species. These aspects will be further investigated as work is continued on biostacks I and II. B IOCO R E EX P E RIM E N'F Five pocket mice were flown in a self-contained unit in the Apollo 17 command module to study the effects of cosmic rays on living tissues, especially the brain. Four of the five mice survived the trip. Processing of the bodies of all five Apollo mice and of a number of control mice is underway. Sectioning of the brains has been delayed pending full analysis of the cosmic ray tracks in the subscalp monitors. An average of 16 tracks/monitor was found for the monitors on the mice that survived the trip. Portions of the scalp of one Apollo mouse have been examined and found to contain some lesions, but a direct relationship between these lesions and cosmic ray hits will have to await further analysis and comparison between locations in the scalp and in the monitors,

Observations of the light flash phenomenon continued during the Apollo 17 mission. As on Apollo 16, the Apollo light flash moving emulsion detector was worn by one crewman for a 1-hr observing session during translunar coast. No results are yet available on the time history of tracks in these emulsions. When available, these data should define the particles responsible for the light flashes. Some statistical data are available now on observations made during the last four Apollo missions. In particular, two items stand out. First, a relatively long period of time is required before the perception of the first event compared to the time between events thereafter. This fact would indicate that dark adaptation is involved and that the events occur in the eye. Second, the length of time before the observation of the first event was longer during transearth coast than during translunar coast; also, the rate of observed events, after the first one, was lower during transearth coast than during translunar coast. The cause of the greatly reduced ability to see the light flashes during transearth coast as opposed to translunar coast is not clear. O R B ITA L G E O LOG Y More than a score of individual investigations of surface and spatial features have been performed so far based on the Apollo 17 crew orbital observations and panoramic and metric camera photographs. The scope of these investigations ranges from studies of the structure of individual craters to studies of the sequences of mare stratigraphy and mare ridges to studies of the solar corona and zodiacal light.

4. Photographic

Summary

M. C. McEwen a and Uel S. Clanton a

The photographic objectives of the Apollo 17 mission were to provide precisely oriented mapping camera photographs and high-resolution panoramic camera photographs of the lunar surface, to support a wide variety of scientific and operational experiments, and to document operational tasks on the lunar surface and in flight, Lunar surface photographs are primarily of three types: (1) operational photographs, to document the condition, performance, orientation, or setting of equipment and the effectiveness of procedures;. (2) scientific documentation photographs, to record samples in their undisturbed condition as well as their location, orientation, and detailed setting or to record features or materials that were not collected; and (3) panoramic views, to provide for the accurate location of traverse stations and to provide the capability to reconstruct the geologic setting of the landing site. Orbital photographic tasks, other than mapping camera and panoramic camera operation, were for both operational and scientific purposes. Orbital science photography planned before the mission included (l) areas of geologic interest; (2)nearterminator areas, where details of relief are enhanced; (3) areas not covered by photography :from other missions; (4)areas in earthshine; and (5)low-lightlevel astronomical phenomena, such as the solar corona and zodiacal light. In addition, film was allotted for crew-option photographs to be taken on the basis of real-time observations, In tables 4-I to 4-III, the Apollo 17 cameras and film types are listed, and a general description of the tasks for which each was used is provided. The color film used in the command module (CM), SO 368, was

intended primarily for well-lighted targets but was used with a high degree of success for target strips that extended almost to the terminator. Earthshine photographs, virtually for the first time on an Apollo mission, have provided usable imagery, including that of lunar surface areas where the crewmen reported seeing possible "flashes." Crew-option photographs include the "flash" areas, lunar surface color boundaries, areas with orange-colored strata, flows, and other features of geologic interest. The lunar surface groundtrack envelope of the Apollo 17 spacecraft is illustrated in section 2 of this report (fig. 2-6). The orbital inclination was approximately 20 ° throughout the first 47 lunar revolutions and was increased to slightly more than 23 ° during revolution 48. The terminator advanced 75 ° across the lunar surface while the Apollo 17 spacecraft was in orbit. A portion of the lunar far side that had not been illuminated during the other J-series missions (Apollo 15 and 16) was in sunlight during the early revolutions of the Apollo 17 spacecraft. The panoramic and mapping cameras were used to photograph a part of this area centered along a line from approximately latitude 23 ° S, longitude 152° W, to latitude 17° S, longitude 180° W. Electric Hasselblad (EL) 70-mm photographs of the same area complement the scientific instrument module (SIM) camera photographs. In the panoramic camera, 1623 images were exposed, of which approximately 1580 are highresolution photographs from lunar orbit. The remainder are transearth coast (TEC) views of the lunar surface. The panoramic camera image is 11.4 by 114.8 cm and, at the 110-km altitude approximated in the near-circular orbit after revolution 12, covers a

aNASALyndon B.Johnson SpaceCenter. 4-1

4-2

APOLLO

1 7 PRELIMINARY

SCIENCE

REPORT

TABLE Camera Electric Hasselblad (EL)

4-1.-Photographic Features

Equipment

Used in the Command Film size and type

Module Remarks Used with 80-ram lens and color film to document operations and maneuvers involving more than one vehicle. Used with appropriate lens-flhn combinations to photograph presclected orbital science lunar targets, different types of terrain at the lunar terminator, crew-option lunar targets, astronomical phenomena, views of the Moon after transearth injection, and the Earth from various distances Used for dim-light photographs of astronomical phenomena, photographs of lunar surface targets illuminated by earthshine, and the Apollo light flash moving emulsion detector Bracket mounted with mirror in command module (CM) rendezvous window to document maneuvers with the lunar module (LM) and CM entry; handheld for other photographs, including subjects inside and o u tside the CM; bracket mounted on sextant to document landmark tracking

21- by 330-km area of the lunar surface. Before revolution 12, the orbit was more highly elliptical, and the dimensions of the lunar surface area depicted vary significantly as a function of position along the groundtrack, Of 3298 mapping camera frames, approximately 2350 contain imagery of the lunar surface. The remaining frames were used for calibration or camera cycling or were exposed over unlighted lunar surface either near terminators or when the camera was used in conjunction with the laser altimeter. The 11.4-cm 2 image of the mapping camera covers a lunar surface area approximately 150 km, or roughly 5 °, on a side at the nominal l l0-kmaltitude, Throughout the lunar orbit phase of the mission, the nominal procedure was to operate the mapping

camera over the entire sunlit which it was used. Panoramic

portion of any pass in camera operation was

more limited because of the much higher rate of film use and because of a 30-min continuous-operation constraint. The prime considerations in the premission task of selecting revolutions on which the SIM cameras would be operated were that the groundtrack be sufficiently offset from other groundtracks to permit coverage of new area and that camera operation be compatible with other mission activities. Mapping and panoramic lunar surface is indicated camera coverage of the in figures 4-1 and 4-2,

respectively. These maps were prepared during the Apollo 17 mission and are based on real-time trajectory data and telemetered camera-function data;

The I 1.4-cm 2 franres with 78-percent forward overlap provide photographs of mapping quality. Data recorded on tile fihn will pernriI reconstruction of lunar surface geometry with a high degree of accuracy.

focal-length lens; 74 ° by 74 ° field of view; a square array of 121 Reseau crosses, 8 fiducial marks, and the camera serial number recorded on each frame with auxiliary data of time, altitude, shutter speed, and forward-motion control setting Part of mapping camera subsystern; 7.6-cm lens; viewing angle at 96 ° to mapping camera view; a square array of 25 Reseau crosses, 4 edge fiducial marks, and the lens serial number recorded on each frame with binary-coded time and altitude Electric; controls in CSM, 61-cm lens; 10046 , by 108 ° field of view; fiducial marks printed along both edges; IRIG a B time code printed along forward edge; data block includes frame number, time, mission data, velocity/height, and camerapointing altitude

mounted on the remote control unit for extravehicular activity (EVA) photographs; used for photography through the LM window and for documentation of surface activities, sample sites, and experinrent installation Handheld; used to photograph distant objects from selected points during the three EVA periods Mounted in the LM right-hand window to record the LM pilot (LMP) view of the lunar scene during descent and ascent and to document maneuvers with the CSM

Hasselblad

DC

Electric; 500-mm Reseau plate

lens;

70 mm, 3401 Plus-X black-andwhite film, AEI 64

DAC

Electric;

10-ram lens

t 6 mm, SO 368 Ektachrome MS color-reversal film, ASA 64

4-4

APOLLO

17 PRELIMINARY

SCIENCE

REPORT

60W

30W

Direction lunarrotation of Approximate (I,5deg/hr rate 0

30E

60E

201

q il ' _ ,___,

"%;

,i':-'i

60W FIGURE 4-1.-Apollo

30W

0

30E

60E

17 mapping camera coverage. The coverage is based on camera on/off times from telemetry, not

minor differences

may become

apparent

between

the

EARTH

ORBIT COAST

AND

TRANSLUNAR

indicated coverage and the actuaI coverage determined from examination of the photographs. Hasselblad EL photographs exposed from the CM total 1170; Hasselblad data camera (DC) photographs exposed from the lunar module (LM) or on the lunar surface total 2422, most of which were taken on the lunar surface. The total number of 35-ram Nikon frames exposed is near 380. Of the 12 magazines of 16-ram film exposed on the Apollo 17 mission, four were used inside the LM and eight in the CM. At the time of preparation of this report, the Apollo 17 photographs had been rapidly screened and the images had been identified and located. Index maps of orbital photographs and tabular indexes with supplemental information for all photographs, both from the spacecraft and the lunar surface, are in preparation,

PHOTOGRAPHY

For the first time in an Apollo mission, the Antarctic continent was visible to and photographed by the orbiting astronauts. A spectacular group of 70-ram Hasselblad EL color photographs exposed in Earth orbit portray the sunlit portion of the Earth from the South Atlantic Ocean across Africa and the Indian Ocean to Australia. Cloud patterns are the subject of several of the photographs. Lift-off is pictured in figure 4-3; figures 4-4 and 4-5 are Earth orbit views. 3;pproximately 1 hr after the translunar injection (TLI) maneuver during the translunar coast (TLC) phase of the mission, the transposition, docking, and extraction (TD&E) maneuvers were executed. In sequence, the TD&E maneuvers included command and service module

PHOTOGRAPHIC

SUMMARY

4-5

on analysis of photographs. Only sunlit coverage is indicated. The area photographed

after transearth injection is not shown.

(CSM) separation

from

the SIVB, a 180 ° _otation

of

LUNAR

ORB IT PHOTOGRAPHY LM TOUCHDOWN

the CSM, docking of the CSM with the, LM, and extraction of the LM from the S1VB. These maneuvers were documented from the CM with both the Hasselblad EL camera and the 16-mm data acquisition camera (DAC). The DAC was bracket mounted, and the views of the LM, SIVB, and Earth in this sequence are mirror images. During TLC, the crew provided extensive descriptions of the Earth surface and of cloud patterns, and the view was repeatedly recorded with the DAC and the Hasselblad camera. Approximately 4.5 hr before lunar orbit insertion, the door that provided protecrive cover to the instruments in the SIM bay was jettisoned; its departure was photographed with the DAC. The hyperbolic trajectory of the SIM bay door eventually carried it beyond the lunar sphere of influence. Figures 4-6 to 4-9 are TLC photographs,

PRECEDING

During the first revolution of the spacecraft about the Moon, the lunar surface was in sunlight from approximately 151 ° W to 29 ° E longitude. As the spacecraft crossed the lunar sunrise terminator, the Hasselblad EL camera was used to photograph the Taurus-Littrow landing site (lat. 20.2 ° N, long. 30.8 ° E) at a very low Sun illumination angle. When the spacecraft passed into sunlight again, near longitude 152 ° W, the panoramic and mapping cameras were switched on to photograph a lunar far-side area where high-quality photographic coverage had not been available previously. To complenrent the SIM camera photographs, the Hasselblad EL camera was used to document the area north of the groundtrack from the vicinity of the crater Galois

4-6

APOLLO

17 PRELIMINARY

SCIENCE

REPORT

60W 40 .....

1_:_ 7 -_

30W i. _

Direction lunar rotation --*.of Approximate rate0.5 deg/hr 0 _7v_: _

30E :,, 1;_,; ,......

60E

20

,_

60W

30W

0

30E

60E not

FIGURE 4-2. Apollo 17 panoramic camera coverage. The coverage is based on camera on/off times from telemetry,

on analysis of photographs. Only sunlit coverage is indicated. The area photographed

after transearth injection is not shown.

FIGURE 4-4.-Great Barrier Reef off the eastern shore of Cape York at the northern tip of Queensland, Australia, photographed during the first revolution of Earth orbit. In this near-vertical view, the shoreline forms an almost north-south line with the south end obscured by part of the spacecraft. The distance between the points at which the shoreline intersects the top and bottom of the photograph is 160 km (AS17-148-22609).

4-8

APOLLO

1 7 PRELIMINARY

SCIENCE

REPORT

FIGURE 4-5.-In this oblique view of the west coast of Africa photographed on the second revolution of Earth orbit, the Cunene River at the right edge marks the border between Angola to the left and Southwest Africa to the right. Punta da Marca, now an island, extends 45 km into the Atlantic Ocean (AS17-148-22623).

FIGURE 4-6.-The LM viewed from the CM shortly after the TLI burn and shortly before the docking and extraction of the LM from the SIVB. Brightly reflective material flaked from the spacecraft fills the field of view around the LM. The circular LM upper hatch, used for transfer of crew and equipment from the LM to the CM, is centered in this view (AS17-148-22687).

FIGURE

4-7.-The

SIVB

after

extraction

of the LM. The

SIVB, 6.6 m in diameter, 18.1 m long, and 11 300 kg in mass (dry), provided the thrust for TLI and was subsequently impacted into the lunar surface to provide a data point for the Apollo 12, 14, 15, and 16 seismometers (AS17-148-22713).

PHOTOGRAPHIC

SUMMARY

4-9

FIGURE 4-8.-Shortly after the LM was extracted from the S1VB, the crew viewed a portion of the Earth from the Mediterranean Sea to India. In Africa, the transition from desert (near the Mediterranean) through steppe and savannah to tropical rain forest (in the lower left corner) is apparent. The Nile River and Delta are clearly visible as are the Gulf of Kutch and the Gulf of Cambay in India (AS17-148-22718).

FIGURE 4-9.-For the first time on an Apollo mission, the Antarctic icecap was visible during the Apollo 17 TLC. This full-disk view encompasses much of the South Atlantic Ocean, virtually all the Indian Ocean, Antarctica, Africa, a part of Asia, and, on the horizon, Indonesia and the western edge of Australia (AS17-148-22727).

4-10

APOLLO

17 PRELIMINARY

SCIENCE

REPORT

Oat. 15 ° S,long. 152 ° W) to near the crater Vil'ev (lat. 6 ° S, long. 144 ° E). The mapping camera was left in operation until the spacecraft passed above the near-side terminator, near longitude 28 ° E. The panoramic camera, constrained to not more than 30 min continuous operation, was turned off near longitude 144 ° E; it was operated again from longitude 122 ° to 95 ° E. The SIM cameras were not operated again until after the LM was on the lunar surface.. Although no additional orbital science photography was scheduled until after the LM landing on revolution 13, a number of crew-option photographs were exposed during the first several revolutions (figs. 4-10 and 4-11). Areas of special interest on the near side and the far side were photographed using the Hasselblad camera with color film or, in the case of near-terminator areas, with high-speed blackand-white film. Separation of the CSM and the LM on revolution 12 was documented with the Hasselblad camera and the DAC from each spacecraft. DAC photographed a mirror image. The CSM \

FIGURE 4-1t.-Earthrise. Shortly after the beginning of revolution 3, the gibbous Earth rising over the eastern limb of the Moon was photographed from the CM. Part of the LM ascent stage is visible in the right foreground. The orientation of the Earth is the same as that in figure 4-10; a comparison of the two photographs clearly shows the eastward rotation of the Earth under the sunset terminator (AS17-151-23188).

FIGURE 4-10.-Earthset. As the CSM and the LM rounded the western limb of the Moon on revolution 2, the crew photographed this unusual view of the gibbous Earth disappearing below the lunar horizon. The north pole of the Earth is toward the top of the photograph. On the left, the relief of the lunar surface near the western limb is sharply etched against the white clouds of the Earth; on the right is the sunset terminator of the Earth (AS17-151-23175).

FIGURE 4-12.-The LM after separation from the CSM on revolution 12. The LM descended to the lunar surface at the Taurus-Littrow landing site on revolution 13 (AS 17-151-23201).

PHOTOGRAPHIC

SUMMARY

4-1 1

FIGURE 4-13.-The CSM, near the center of the photograph, is framed against the flat valley floor at the TaurusLittrow landing site in this dramatic west-looking view from the LM shortly after separation on revolution 12. South Massif is the large mountain just beyond the CSM. The light-colored material that extends north (to the right) onto the valley floor from South Massif is the Rock Slide, and, opposite the Rock Slide, the mountain on the north side of the landing site is North Massif. The low hill nearly centered in the valley beyond the Rock Slide is Family Mountain. The crests of South Massif and North Massif are 2500 and 2100 m, respectively, above the landing site. To the west, color differences in the surface of southern Mare Serenitatis are evident even in this highly obliquephotograph(AS17-147-22464).

2 FIGURE 4-15.-The LM on the lunar surface at the Taurus-Littrow landing site. This photograph is a 49X enlargement of a portion of a panoramic camera frame that was exposed on revolution 15 when the Sun elevation at the site was 15°. The LM is the bright spot in the center; its shadow extends outward 5° north of west. The photograph represents a lunar surface area 300 m on a side (Apollo 17 panoramic camera frame ASt7-2309).

The orbit of the CSM was circularized during revolution 12. On the 13th revolution, the CSM DAC was mounted on the sextant to document the tracking of two landmarks, the second of which was at the Taurus-Littrow landing site. Simultaneously, the powered descent of the LM, from time of pitchover to touchdown, was recorded by the LM DAC, mounted in the right side window. The LM in orbit is pictured in figure 4-12. Figures 4-13 and 4-14 are orbital photographs of the landing site, and figure 4-15 is an enlargement showing the LM on the lunar surface.

LUNAR

SURFACE

PHOTOGRAPHY

FIGURE

4-14.-The

landing site from higher altitude on

During the stay on the lunar surface, the commander (CDR) and the LM pilot (LMP) exposed more than 2200 frames in their Hasselblad DC's. One magazine of DAC commander's initial f'dm was used to record the activities on the lunar surface as the LM DAC was not

revolution 74. Topographic details are obscured and albedo differences are enhanced by the high Sun angle at the time this photograph was taken. The bright crater north and west of the landing site is Littrow B (AS17-148-22770).

viewed from the LM window; used again until lift-off.

4-1 2

APOLLO

17 PRELIMINARY

SCIENCE

REPORT

The crew began photographic documentation of the landing site as they viewed it from the LM windows shortly after touchdown (fig. 4-16). Sitedocumentation photography was a continuing operation throughout the lunar surface stay. Figure 4-17 illustrates the intense activity of the three periods of extravehicular activity (EVA) at the site as it appeared from an LM window shortly before lift-off, Real-time observations of lunar surface activities were provided scientists and engineers on Earth by the television (TV) camera mounted on the lunar roving vehicle (LRV). The lunar surface documentary photographs taken in the vicinity of the LM included the checkout drive of the LRV (fig. 4-18) and the traditional salute to the flag (fig. 4-19) taken during EVA-1. Before

EVA-2, the LMP was photographed with the equipment required for the EVA (fig. 4-20). The CDR also documented their repair of the LRV fender that was broken during EVA-1 (fig. 4-21). A photograph of the Earth above the LM (fig. 4-22) was taken shortly before EVA-2 closeout. The deployment of the lunar surface experiment equipment was documented with 70-mm Hasselblad photographs. Figures 4-23 to 4-27 show the Apollo lunar surface experiments package (ALSEP) site and several individual pieces of scientific equipment. Sample documentation includes photographs of boulders from which samples were collected (figs. 4-28 and 4-29) and photographs that illustrate the use of sampling tools (figs. 4-30 and 4-31). Figure 4-32 is a typical presampling photograph. Perhaps the most

FIGURE 4-16.-A view of the Taurus-Littrow area from the LM window taken just after touchdown on the lunar surface. Tile shadow of the LM is along the lower left margin of the photograph. Family Mountain, on the horizon from the left margin to the center of the photograph, is almost 11 km distant; its crest is approximately 1000 m above the valley floor. The dark-gray basalt fragments on the lunar surface appear to be white in this down-Sun photograph (AS 17-147-22470).

PItOTOGRAPHIC

SUMMARY

4-1 3

FIGURE

4-17.

A

view

of

the

landing site from the LM window taken just before lift-off. Compare this photograph with figure 4-16. The intense activity in the vicinity of the LM is indicated by the footprints and the LRV tracks. The Apollo lunar surface experiments package (ALSEP) components can be seen in the distance. The craters seen in the foreground of figure 4-16 are not visible in this photograph, which was taken at a higher Sun angle (AS17-145-22200).

FIGURE

4-18.-Shortly

after

dethe of the

ployment, the CDR drove LRV through a series maneuvers to check out performance The LRV

":

of the vehicle. was then loaded

with tools, experiment hardware, a TV camera, and antennas. South Massif, the crest of which is 2500 m above the valley floor, forms the skyline 5 km behind the LM. The bands of dark gray are LRV tracks; bootprints in the lunar surface are visible near the right margin of the photograph (AS 17-147-22527).

4-14

APOLLO

17 PRELIMINARY

SCIENCE

REPORT

FIGURE

4-19.-The

CDR

salutes

the

flag of the United States implanted at the Apollo 17 landing site. Approximately 3 km in the distance, the 2t00-m-high North Massif forms the skyline. The LRV is visible at the left margin of the photograph. The flag pictured was the backup flag for the Apollo 11 mission and was in the Mission Operations Control Room from July 1969 until just before the Apollo 17 mission (AS17-134-20386).

FIGURE 4-20.-The LMP stands in front of the LRV at the start of EVA-2. Sample bags are attached to the remote control unit on his chest. The sample collection bag is attached to the right side of the portable life-support system (PLSS). The cuff checklist, an outline of activities, is on his left wrist. The LRV sampler hangs in front of fire astronaut. The gold-colored TV camera is at the right edge of the photograph. The reflection of the CDR can be seen in the LMP's visor (AS17-140-21386).

FIGURE 4-21.-The partial loss of the right rear fender during EVA-1 threatened to limit the use of the LRV. Without complete fenders, the wire mesh wheels threw a plume of lunar dust across the crew and the LRV. At the beginning of EVA-2, the crew replaced the missing section using maps, tape, and two clamps from the LM. The repairs proved to be satisfactory, and no further problems were experienced. The LMP sits in the LRV (AS17-137-20979).

PHOTOGRAPHIC

SUMMARY

4-1 5

FIGURE

4-23.

The gnomon

with color chart sits next to geophones, indicated

one of the lunar seismic profiling FIGURE 4-22.-A half Earth hangs over the LM on the lunar surface (AS17-134-20463).

by the orange flag. The gold-colored, rectangular object near left center is the ALSEP central station; the white antenna extending above the central station telemeters data to Earth from each of the surrounding experiments. North Massif, 3 km in the distance, forms the skyline. On the slope of North Massif, to the right of the LRV, is a track made by a massive boulder as it rolled down the side of the mountain. The sharpness of the track have been in its present time (AS17-147-22549). suggests position that the boulder may only a relatively short

FIGURE 4-24.-A gold-colored Mylar transport bag covers the top of the lunar neutron probe (LNP) for temperature control during the 40-hr emplacement of the probe in the Moon. The LNP is designed to obtain data on neutron capture rates in the lunar regolith as a function of depth. The LNP was emplaced through the treadle assembly into the hole drilled for the core sample. The borestem and corestem rack is visible at the right margin of the photograph. Tile Apollo lunar surface drill power head lies on the lunar surface behind the rack. The ALSEP equipment is set up in the background. The Sculptured Hills and South Massif form the horizon (AS 17-134-20505). FIGURE 4-25.-The CDR inserts a heat flow probe into the borestem during the deployment of the ALSEP. The drill and rack with additional borcstems and corestems are to the left of the astronaut. Tile heat flow experiment measures the heat flow from the interior of the Moon (AS 17-136-20695).

4-16

APOLLO

17 PRELIMINARY

SCIENCE

REPORT

FIGURE 4-26. The problem of distance perception on the Moon is well illustrated in this photograph. The distance to the LRV and the surface electrical properties (SEP) experiment is 35 m; the distance to the LMP is 70 m. The distance to the LM is 150 m; to the ALSEP, 350 m. Family Mountain is 11 km beyond the LRV, and South Massif is behind the LM. The wire in the foreground is part of the dipole antenna of the SEP experiment• Compare this photograph with figure 4-27 and note the relationship ofsizeanddistance(AS17-134-20435),

FIGURE 4-27.-The LMP emplaces the SEP experiment. The equipment shown, which supports the experiment, includes a transmitter to generate a signal and a dipole antenna that is laid out on the lunar surface by the crew. A receiver is carried on the LRV. The interference pattern of the transmitted waves provides information about the interior of the Moon. The restricted mobility caused by the pressure suit is illustrated by the body position required to make leveling corrections. The wires in the foreground are part of the SEP experiment antenna. South Massif forms the skyline (AS17-134-20440).

FIGURE 4-28. The massive, broken boulder at station photograph. Scoop marks in the debris on the side of the sample collected by the LMP. The boulder is a breccia, a other rocks• The LRV, with the antenna pointed toward the boulder. South Massif, 8 km distant, forms the right forms the left half (AS17-140-21493 and 21497).

6 is shown in this composite boulder mark the location of a rock composed of fragments of Earth, is parked to the right of half of the skyline; East Massif

PHOTOGRAPHIC

SUMMARY

4-1 7

FIGURE 4-29.-Sampling boulder behind the

at station LMP. The

6 centered around the dark bootprints in the

FIGURE rocks

4-30.-The LMP uses the rake to collect a sample of ranging from 1 to 4 cm in diameter. A soil sample

foreground and near the base of the boulder indicate the areas of astronaut activity. The LRV is visible at fire left side of the photograph (AS17-146-22294).

was collected in the same area. The Hasselblad camera is attached to the remote control unit; tile PLSS and the oxygen purge (AS 17-134-20425). system comprise the backpack

FIGURE 4-31.-The LMP uses the scoop to collect a sample at station 5. The high density of boulders along the rim of Camelot Crater is shown in this photograph (AS17-145-22157).

FIGURE 4-32,-The gnomon with color chart marks tire location from which a sample will be collected, The white areas on the boulder to the left of the gnomon are clasts; the clasts are bound in a fine-grained gray matrix (AS17-137-20963).

4-18

APOLLO 17 PRELIMINARY SCIENCE REPORT looking oblique), 27/28, 28/29, 36 (south-looking oblique), 38, and 49. The designation "13/14" means that the camera was turned on near the end of revolution 13, which ends at 180°, and continued in operation during revolution 14 to the terminator. In several of these passes, the camera was also operated over unlighted lunar surface to obtain laser altimeter data. The north- and south-looking oblique photographs were exposed when the CSM was rolled 40°; the oblique photographs show the lunar surface to the horizon, approximately 20 ° from the spacecraft nadir. The panoramic camera was operated on revolutions 13/14, 15, 29, 36 (a cycle of five frames to prevent film set; south-looking oblique), and 49. Hasselblad EL stereophotographic strips, exposed with either the 80- or the 250-mm lens and color film, are as follows: on revolution 16, a far-side strip at the spacecraft nadir from east of the crater Aitken to the crater Marconi; on revolution 17, a series south of the groundtrack from the crater Sniadecki to a point south of the crater Marconi; on revolution 25, the landing site and southwestern Mare Serenitatis; on revolution 28, a series south of the groundtrack from the crater Picard to Promontorium Archerusia on the

widely known and highly publicized samples of the Apollo 17 mission were from the "orange soil" found at Shorty Crater during EVA-2 (figs. 4-33 and 4-34). Features too large to record in single frames were documented in partial panoramas (fig. 4-35). The general setting of a station was routinely recorded in a complete 360 ° panorama. The 500-ram lens provided the capability to record distant features in single frames (fig. 4-36) or in partial panoramas, After completion of the EVA-2 sampling activities, the LRV was parked east of the LM, and the Houston-controlled TV camera provided live coverage of the final closeout and of the ascent stage lift-off from the lunar surface, LUNAR ORBIT PHOTOGRAPHY FROM LM TOUCHDOWN TO RENDEZVOUS AND DOCKING All orbital photographic activities in the period between LM touchdown and rendezvous and docking (revolutions 13 to 52) were as planned. The mapping camera was operated from terminator to terminator on revolutions 13/14, 14/15, 23/24, 26/27 (north-

FIGURE 4-33.-The orange soil on the rim of Shorty Crater can be seen on both sides of the LRV. The rim of the crater extends from the left foreground to the middle right edge of the photograph. Samples were collected between the LRV and the large boulder. (See fig. 4-34.) The low mountain centered on the horizon is Family Mountain, 6 km in the distance (AS17-137-21011).

FIGURE 4-34.-A closeup of the trench dug in the orange band of soil. Behind the gnomon is the boulder pictured in figure4-33 (AS17-137-20990).

PHOTOGRAPHIC

SUMMARY

4-19

FIGURE 4-35.-This panorama at station 9 shows the unique morphology of the 80-m-diameter crater Van Serg. The rough, blocky rim and floor indicate that the crater is relatively young. Locations such as this are excellent sampling sites. North Massif, 3 km in the distance, forms the skyline (AS17-142-21801, 21805, 21807, and 21811).

crater Aitken on revolution 37. The Hasselblad camera was also used repeatedly during revolutions 13 to 52 for crew-option documentation of other areas of interest. Figures 4-37 to 4-42 are photographs of lunar far-side features; figures 4-43 to 4-49 include nearside features; figure 4-50 is a photograph of an earthshine-iUuminated area; and figure 4-51 is a photograph of a near-terminator area. The solar corona was photographed at spacecraft sunrise on revolution 25 using the bracket-mounted Hasselblad camera with 80-mm lens. The Nikon camera was used to photograph red, blue, and polarizing filters the zodiacal light; were used for these

FIGURE 4-36.-One of a series of photographs taken by the CDR, while standing at the base of the North Massif, of the landing site and South Massif using the 500-mm photographic lens. This photograph of the valley floor shows the LM some 3 km in the distance. The large blocky craters to the right of the LM are Camelot, approximately 600 m in diameter, and Horatio, approximately 400 m in diameter. South Massif, 8 km in the distance, appears steeper in this photographic view (AS17-139-21205). south margin of Mare Serenitatis; on revolution 29, a series north of the groundtrack from the crater Love to the crater Saenger and a second strip north of the groundtrack from eastern Mare Crisium to the crater Bessel; on revolution 36, a south-looking series from the crater Van de Graaff to the crater Serpiensky; and, on revolution 39,a strip from the crater Tacquet to an area north of the crater Eratosthenes. Near-terminator areas photographed included Mare Serenitatis on revolution 17, Montes Haemus and northern Mare Vaporum on revolution 29, and the

exposures. Earthshine-illuminated areas photographed with the Nikon camera include the craters Eratosthenes, Copernicus, Grimaldi, and Riccioli, the Reiner 3' prominence, and Mare Orientale. The Nikon camera was also used to document near-side and far-side near-terminator areas and other areas determined by the CM pilot (CMP) to be of interest. The sextantmounted DAC was used to document the tracking of two landmarks on revolution 50. As the CSM passed over the landing site during revolution 51, the LM ascent stage separated from the descent stage and lifted off from the lunar surface (fig. 4-52). The LM DAC, bracket mounted in the LM window, photographed lunar surface features, including the descent stage, the ALSEP instruments deployed at the landing site, and LRV tracks, as the LM passed above them (fig. 4-53). The rendezvous of the LM and CSM was documented with the DAC and Hasselblad from the CM but only with the Hasselblad

4-20

APOLLO

17 PRELIMINARY

SCIENCE

REPORT

FIGURE

4-37.-North-looking,

high-oblique

view of the lunar far side near the lunar sunset terminator smaller craters is Doppler, 100 km in diameter. The is

on the first revolution. The foreground crater containing several centered at latitude 13 ° S, longitude 160 ° W, and approximately

larger crater to the north which extends from the left side to the right side of the photograph Korolev, approximately 450 km in diameter (AS17-151-23112).

FIGURE

4-38.-The

lunar

far-side

crater

Van de

Graaff, centered at latitude 28 ° S, longitude 173 ° E, is the large, flat-floored double crater in this south-looking, high-oblique view. Its long dimension is approximately 270 km. Adjoining Van de Graaff on the southeast is the crater Birkeland, which has terraced walls and a central peak. The circular, mare-filled crater on the right horizon is Thomson (AS17-150-22959).

PHOTOGRAPHIC

SUMMARY

4-21

FIGURE 4-39.-This unnamed crater with a hummocky floor is in a far-side area that was very poorly documented before the Apollo 17 mission. The low-oblique view is to the southeast. The center of the 40-km-diameter crater is at latitude 21 ° S, longitude 169 ° W. Note the scarp that crosses the crater floor from the shadow at the right middle through the embayment in the craterwall at upper left and continues into the terrain outside tile crater. In the upper right corner, the north rim of the crater Sniadecki is visible (AS17-151-23193).

FIGURE 4-40.-The circular, flat-floored, mare-filled crater that extends beyond the left and right edges of this photograph is Thomson, a 150-kin-diameter crater near latitude 32 ° S, longitude 166 ° E. Beyond Thomson to the south is the southeastern quarter of Mare Ingenii. The shadow in the lower left corner is in the southwest wall of Van de Graaff. The crater foreground (AS 17-153-23543). Zelinsky is in the right

FIGURE

4-41.-Aitken,

a far-side

crater

located

at latitude

17 ° S, longitude 173 ° E, measures approximately 150 km from rim to rim. In this mapping camera photograph, exposed during revolution 15, north is at the top. Aitken is characterized by a flat, low-albedo, sparsely cratered floor, by a central peak, and by terraced walls. Ponded, marelike material is evident at various levels in the terraced walls as well as in smaller craters nearby. Details of a part of the eastern wall and floor are shown in figure 4-42 (Apollo 17 mapping camera frame AS 17-0481).

4-22

APOLLO

17 PRELIMINARY

SCIENCE

REPORT

FIGURE

4-43.-Southern

Mare

Serenitatis

(foreground),

western Mare Tranquitlitatis (left), and southeastern Montes Haemus (center). In this oblique mapping camera photograph, the view is almost due south. The 50-kindiameter crater Plinius is at the left edge; at the right edge, the bright crater with the excluded-ray zone is Menelaus, 25 km in diameter. Note that the Rimae Plinius and the Rimae Menelaus, roughly concentric to the southern edge of Mare Serenitatis, are confined to the area of low alhedo (Apollo 17 mapping camera frame AS17-2415).

FIGURE 4-42.-This photograph of a segment of the eastern wall and floor of Aitken (fig. 4-41) was exposed in the Hasselblad camera with a 250-mm lens. North is at the top of the photograph. The topographic features on the crater floor that resemble the wrinkle ridges common in lunar maria can be seen to continue into and across the hummocky, higher albedo wall (AS17-149-22796). material of the lower crater

FIGURE 4-44.-Northwest-looking, low-oblique view of the crater le Monnier approximately 190 km north of the Apollo 17 landing site on the east margin of Mare Serenitatis. The Russian spacecraft Lunokhod 2, an Earth-controlled roving vehicle, landed in le Monnier January 15, 1973. The marelike flat floor of the 70-krn-diameter crater has the low albedo characteristic of the surface material bordering Mare the dark surface material bordering tatis can be seen in the upper photograph. The crater Littrow D Serenitatis; some of eastern Mare Serenileft corner of the is in the right foreLittrow II lower left

ground; between it and le Monnier, Rima extends from the middle right to the (AS17-153-23487).

PHOTOGRAPHIC

SUMMARY

4-23

FIGURE 4-45.-An area of orange-hued material west of the crater Sulpicius Gallus. All three astronauts saw orangehued material in and around craters in this area and could see orange talus on the slopes in the elongate crater just above right center. Many of the smaller craters, particularly in topographically low areas, are surrounded by the orange-hued ejecta. In this near-vertical 250-mm Hasselblad photograph, north is at the top. The elongate crater, situated at latitude 20 ° N, longitude 10.5 ° E, is 6 or 7 km long and is approximately 40 km west of Sulpicius Gallus. Rima Sulpicius Ganus I crosses the upper right corner. The Montes Haemus are in the lower left (AS 17-149-22882).

FIGURE 4-46.-This southeastward oblique view shows the setting of the area pictured in figure 4-45. The Rimae Sulpicius Gallus converge on the crater Sulpicius Gallus in the upper middle. The Montes Haemus define the southwestern border of Mare Serenitatis along the right side of the photograph. The bright crater at the right edge is Sulpicius Gallus M. Note the unusual crater at left center with a dark rim and light ejecta (AS17-151-23258).

FIGURE 4-47.-The D-shaped feature in the center of this photograph was first seen in Apollo 15 panoramic camera photographs. Situated at latitude 18 ° N, longitude 5 ° E, the feature measures approximately 3 km along the straight edge and lies below the level of the surrounding dark, marelike material. The CMP has described the pale-blue color seen in this and other feature as accurate (AS17-152-23287). photographs of the

4-24

APOLLO

! 7 PRELIMINARY

SCIENCE

REPORT

FIGURE 4-48.-Proclus, the most prominent excluded-ray-zone crater on the near side of the Moon, has been difficult to photograph successfully because of the brightness of its rays. In this near-vertical photograph, interior details are clear despite the relatively high Sun angle when exposed on revolution 28. North is at the top of the photograph. The object at the right is the CSM EVA floodlight (AS17-150-23046).

FIGURE

4-49.-This

spectacular

panoramic

view

of the

eastern

limb

of

the Moon

was exposed

when

the CSM was in a

pitched-up attitude 290 ° . The entire

during revolution 62. The panoramic camera was pointing along the groundtrack at an azimuth of area of Mare Smythii, more than 400 km from left to right, is visible. In the near field, the

PHOTOGRAPHIC SUMMARY

4-25

from the LM; again, the CSM DAC had a mirror view of the LM and lunar background. On revolution 52, the CSM maneuvered to an attitude that would permit inspection of the SIM bay from the LM, and both spacecraft were photographed with the Hasselblad cameras (figs. 4-54 and 4-55). Much of the area south of the groundtrack from the eastern margin of Mare Crisium to the crater Copernicus was also documented with an LM Hasselblad (fig. 4-56). The CM TV provided Earth a view of the LM during docking maneuvers.

oblique attitude when the mapping camera was switched on near longitude 107° E. With the camera in operation, the CSM began a maneuver to the 40 ° south-looking oblique attitude near longitude 65 ° E and continued in that attitude to the terminator. The last two periods of mapping camera operation in lunar orbit were terminator-to-terminator passes on revolutions 66 and 74. The panoramic camera was operated on revolution 62 from near longitude 132° E to approximately 95 ° E, during which period the CSM was in a pitched-up attitude. As the CSM passed over the landing site on revolution 62, 11 frames were exposed with the camera in the monoscopicmode. An area from Montes Apenninus across southern Mare Imbrium to the terminator was photographed with the Hasselblad camera and color film on revolution 65. Scheduled near-terminator photography was accomplished on revolution 62 near the craters Gagarin and Lambert, on revolution 66 near the crater T. Mayer, and on revolution 74 west of the crater Brayley.

LUNAR ORBIT PHOTOGRAPHY AFTER RENDEZVOUS AND DOCKING After docking on revolution 52 and transfer of the crew and equipment to the CSM from the LM, the LM ascent stage was jettisoned on revolution 54. The receding LM was photographed with CM DAC and the Hasselblad camera. The mapping camera was operated from terminator to terminator on revolution 62. From the far-side terminator to near longitude 90 ° E, the CSM was pitched up, and the tilt of the resultant forwardlooking oblique photographs varies somewhat with longitude. Normal vertical orientation of the SIM cameras was attained near longitude 90 ° E and was maintained throughout the remainder of the pass. On revolution 65, the CSM was in a 40 ° north-looking

TRANSEARTH ENTRY

COAST AND EARTH PHOTOGRAPHY from the Moon (TEl) maneuver,

As the CSM receded rapidly following the transearth injection

150-km-diametercrater Hirayama (centered at lat. 6° S, long. 93° E) extends acrossthe middle one-third of the bottom of the photograph. The bright rays in the extreme left corner are from a crater near latitude 15.5° S, longitude 87.5° E. The crater Dreyer (lat. 10° N, long. 96° E) is just outside the extreme right corner (panoramic camera frame AS17-2871).

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FIGURE

4-50.-Mare

Orientale

in

earthshine.

In

this

south-looking, high-oblique, 35-mm photograph, two of the rings of Mare Orientale are distinctly visible. The photograph includes the area in which the CMP reported seeing a possible light flash. The mareUke area in the middle foreground is Lacus Autumni. Beyond it is Lacus Veris, at the south end of which is the crater Eichstadt K. The Montes Rook delineate the inner of the two rings pictured here. The outer ring, to the left, is marked by the Montes Cordillera (AS 17-158-23902).

FIGURE 4-52.-Lift-off of the LM ascent stage. This photograph was made from the color TV picture transmitted from the Houston-controlled TV camera mounted on the LRV. The LM descent stage remains on the lunar surface (S-72-55421).

FIGURE 4-53.-This 16-ram frame was exposed in the LM DAC from the ascent-stage LMP window shortly after lift-off. The LM descent stage is at the lower left margin of the photograph, and the ALSEP instruments are visible near the upper left corner, approximately 190 m and slightly north of west from the LM. The irregular dark lines between the LM and the ALSEP instruments are LRV tracks. The largest crater in the field of view, at the upper right corner of the photograph, is Rudolph, approximately 50 m in diaineter (Apollo 17 16-mm camera, magazine Q).

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FIGURE 4-54.-The LM ascent stage pictured while stationkeeping with the CSM on revolution 52. The rendezvous radar antenna at the at the top of the LM is pointing CSM. The bell of the ascent

propulsion engine is visible at the bottom of the spacecraft and, above it, the square hatch through which the crew egressed to the lunar surface. Above and to the viewer's right of the hatch, the commander's head is in sunlight in the triangular window. After docking and transfer of the crew and equipment to the CM, the LM ascent stage impacted into the lunar surface near the Apollo 17 ALSEP to provide a data point for the seismometer (AS17-149-22859).

FIGURE

4-55.-The

CSM viewed

from

the LM. While stationkeeping before docking with the LM on revolution 52, the CMP maneuvered the CSM to allow inspection of the SIM bay by the LM crew. The mapping camera film cassette, retrieved by the CMP during TEC, is under the dark cover in the near left corner of the SIM bay. The panoramic camera film cassette is under the square dark cover directly behind the mapping camera cassette. The docking probe is at the apex of the CM. The view is to the southeast; the number "23" at the bottom of the picture is centered in the crater Lick on the southern edge of Mare Crisium. The dark lunar surface area on the horizon at the upper right is (AS17-145-22257). Mare Fecunditatis

PHOTOGRAPHIC

SUMMARY

4-29

FIGURE 4-56.-This high-oblique view from the LM after lift-off from the hmar surface includes the craters Eratosthenes, 60 km in diameter, at left center, and Copernicus on the horizon at the right. The view is to the southwest from :_outhern Mare Imbrium. To the left of Eratosthenes is the southern end of Montes Apenninus. Patterns of secondary craters are emphasized in this low-Sun-angle photograph (AS17-145-22285).

the crew photographed the lunar surface with the DAC and with the Hasselblad camera, using the 80and the 250-mm lenses (figs. 4-57 to 4-59). The crewmen also photographed the crescent Earth with the Hasselblad camera and the DAC. The switched mapping and panoramic cameras on as the CSM passed over the sunlit were lunar

surface shortly after the TEl burn. Images of the lunar surface were recorded on the 17 remaining panoramic camera frames and on 107 mapping camera frames before the lunar disk drifted from the field of view. The TEC EVA, in which the CMP retrieved the mapping camera and panoramic camera film canisters from the SIM bay, was documented with the DAC and the Hasselblad camera (fig. 4-60). FIGURE 4-57.-View of the northeastern quadrant of the Moon taken during TEC. Mare Crisium is the circular feature at the right; from bottom center up are Mare Fecunditatis, Mare Tranquillitatis, and Mare Serenitatis. The Apollo 17 landing site at the southeastern margin of Mare Serenitatis is easily distinguished by the very dark mantling material. The bright-rayed crater to the left of Mare Crisium is Proelus (AS l 7-152-23339). The fireball accompanying the CM entry into the Earth atmosphere was photographed with the DAC, as was the deployment of the drogue and main parachutes. Approximately 13 min after Earth entry interface, the CM splashed down in the South Pacific Ocean near latitude 8 ° S, longitude 166 ° W (fig. 4-61 ).

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FIGURE

4-58.-A

TEC view of Mare Australe.

The center

of this view is near latitude

35 ° S, longitude

90 ° E.

In the upper niiddle, the large crater with dark material on its floor near both the left and right walls is Humboldt, centered at latitude 27 ° S, longitude 81 ° E (AS17-152-23288).

PHOTOGRAPHIC

SUMMARY

4-3 !

FIGURE 4-59.-A TEC view of the almost-full lunar disk. The dark-floored crater Tsiolkovsky is near the terminator at lower right. Humboldt Crater is to the left of and below center. Part of Mare Serenitatis is visible on the horizon at the top just to the left of center (AS17-152-23308).

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FIGURE 4-60.-The CMP is pictured ing his TEC EVA to retrieve . canisters from the mapping

durfilm

and pano-

ramic cameras in the SIM bay of the service module (SM). The CMP is holding a handrail on the SM, and his body is extended over the open SIM bay. The mapping camera film canister is near his left elbow. At the rear of the 9 SM, the lunar sounder experiment VHF antenna extends toward the top right corner of the photograph (AS17-152-23391).

FIGURE 4-61.-The Apollo 17 CM nears splashdown in the South Pacific Ocean within approximately 1 km of the target point. Splashdown was at 07:24:59 G.m.t., December 19, 1972, 304 hr 32 min after lift-off from the NASA John F. Kennedy Florida (S-72-55834). Space Center,

APPENDIX

Near-Terminator

and

Earthshine

Photography

James W. Head a and Douglas Lloyd b

The purposes of this paper are to illustrate and describe two types of special photograph (near terminator and earthshine) taken during the Apollo 17 mission and to point out potential areas of its usefulness to encourage full utilization of the Apollo 17 photographs in scientific investigations. Where appropriate, some description and preliminary interpretation are given to demonstrate the potential of various photographs, Lunar surface photographs taken in the vicinity of the sunshine terminator provide important information that is often unavailable on photographs taken at higher Sun-elevation angles (such as Lunar Orbiter and most Apollo orbital photographs). Features that are particularly enhanced include those of low relief (such as mare flow fronts), craters of different morphology (rimless depressions, secondaries, etc.), areas of contrasting crater densities, and small-scale structures occurring on other low-relief features (such as mare ridges). Technical details of Apollo near-terminator photography are given in references 4-1 to 4-4. During Apollo 17, two magazines of very-highspeed black-and-white (VHBW) film (2485)were exposed using the Electric Hasselblad (Et,) camera on 70-mm film format. Photographs were also obtained under earthshine conditions in areas near the crater Copernicus, in western Oceanus Procellarum, and around the Orientale basin. Technical details of these photographs are described in reference 4-2. During the Apollo 17 mission, VHBW 35-ram film was exposed with a Nikon camera.

NEAR-TERMINATOR Apollo

PHOTOGRAPHY Site

17 Landing

A near-terminator photograph of the Taurus-Littrow highlands and the Apollo 17 landing site (designated by the arrow) is shown in figure 4-62. The ejecta blanket of the crater Vitruvius (in the lower left, approximately 30 km in diameter) is embayed by smooth mare material, thus indicating a premare age for the crater. The differences between terrain types are enhanced in this low-Sun photograph. The flat, sparsely cratered mare regions around

FIGURE 4-63.-Mosaic of photographs of a portion of Mare Imbrium just north of the crater Euler showing multiple flow lobes and flow fronts. Distance from lower left to upper right is approximately 110 km (AS 17-155-23714 to 23716).

PHOTOGRAPHIC SUMMARY Vitruvius (in the lower right of the photograph) are in contrast with the pitted, more hummocky, cratered terrain of the upland plains. The 10- to 20-km-diameter, smooth-sided massive mountain blocks (massirs) around the landing site also stand in marked contrast to the timer-textured, domical, somewhat lineated Sculptured Hills, which make up the majority of the highlands in figure 4-62. Flow Lobes and Flow Fronts

4-35

narrows and sharpens to the left, and finally emerges as a zigzag scarp-like ridge. The much broader mare arch to the north shows a somewhat similar trend with the mare ridge being even more distinct as it crosses from one side of the arch to the arch axis. Several apparently be seen. Potential flooded craters (arrows) also can

Volcanic

Source Areas

A series of overlapping flows and flow fronts is located in Mare Imbrium, north of the crater Euler (fig. 4-63). These trend to the north and contain a wide variety of leveed flow channels (lower left). The detailed sequence and history of these particular flows have been studied by Schaber (ref. 4-5). Although some of the major flow fronts have been visible on higher Sun photographs, the detailed structure and stratigraphy could not have been worked out without thelow-Sun photographs, Mare Ridges A series of structures associated with mare ridges, which are typical of many mare structures, is shown in figure 4-64. Two broad mare arches (ref. 4-6) are visible. The lower, narrower arch is broad at the right,

Several features of possible volcanic origin (fig. 4-65) are located in a group in southwestern Mare Imbrium. The area is characterized by a series of low hummocky hills; a large, central, irregular rimless depression; a series of crater chains; numerous meandering scarps; a long arcuate rille at the southeastern boundary; and a series of cone-like structures with central craters leading in a chain away from the northern end of the complex (base of fig. 4-65). The assemblage of volcanic structures located in this area suggests that it may have been a center of mare volcanic activity. Mare Albedo and Structure Boundaries

Low-Sun photographs enhance the contrast between major mare units, such as the central fill of

FIGURE 4-64.-Mare arches and ridges (AS17-155-23767).

FIGURE 4-65.-Possible center of mare volcanic activity in southwestern Mare hnbrium. South is at the top; appro:,dimate width of center area is 45 km (AS17-155-23736).

4-36

APOLLO 17 PRELIMINARY SCIENCE REPORT to the left. These mare domes may represent the lunar equivalent of shield volcanoes and may be sources for some of the mare lavas. A second type of domical mare structure is visible in southwestern Mare Imbrium near the crater Diophantus (figs. 4-68(a) and (b)). This structure (seen

Serenitatis and its surrounding dark annulus (fig. 4-66). The dark annulus, a low albedo unit, partially lines the inner edge of Mare Serenitatis and has been mapped as Eratosthenian in age, while the higher albedo central mare fill has been mapped as Imbrian in age (ref. 4-7). However, the dark annulus in southern Serenitatis (lower half of fig. 4-66) is laced with linear rilles that terminate at or are embayed by the central mare unit. Also, secondary craters from the crater Plinius (just off the photograph at the lower right) occur up to the boundary with the central mare but not on the other side. These relationships strongly suggest that the dark annulus predates the central mare of Serenitatis, at least in this area. Domical Structures in Maria

Two general types of domical structures occurring in the maria are enhanced by low-Sun photographs. Low, broad circular domes with or without central pit craters form one type; examples from northern Mare Tranquillitatis are visible in figure 4-67(a) (arrows). A second example is visible west of the crater Copernicus near T. Mayer (fig. 4-67(b)); here a sinuous rille winds around the base of a low 15-km-diameter mare dome located near the base of a highland ridge. The dome has a central pit (tip of arrow). A second broad dome with an elongate central pit is just

FIGURE 4-67.-Domical structures in lunar maria. (a) Domes in northern Mare Tranquinitatis (arrows). The domes average approximately 5 to 10 km in diameter (AS17154-23604). (b) Domes near the crater T. Mayer. The dome designated by the arrow is approximately 15 km in diameter (AS17-155-23739).

]PHOTOGRAPHIC under two different low-Sun conditions)is characterized by an irregular scarp-like outline, central hill and groups of satellite hills, and various associated rilles. No obvious central pit can be identified. The sinuous rille visible here (fig. 4-68) terminates at the base of the domical structure, crosses over the crest adjacent

SUMMARY

4-37

to the central hiils (just outside the figure), and terminates again at the northern end of the structure. The other rille apparently lies at the crest of the structure and may be structural in origin. A number of these features suggest that this mare dome may be the result of differential settling of mare lavas rather

FIGURE 4-68.-Domical mare structure under different low-Sun conditions. (a)Domieal mare structure in southwest Mare Imbrium near Diophantus. The sinuous rille is approximately 600 m wide (AS17-155-23755). Co)Same area as shown in part (a) but at a lower Sun angle (AS17-155-23749).

FIGURE 4-69.-Low-Sun photographs enhancing features associated with sinuous rilles. (a) Rilles and rimless depressions north of Mare Vaporum. The width of the area shown is approximately 25 km (AS17-154-23679). (b) Sinuous rille and mare ridge under near-terminator conditions (AS17-155-23723).

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than extrusive volcanic circular mare domes.

buildup,

as envisioned

for the

Sinuous

Rilles

Figure 4-69 shows some of the features associated with sinuous rilles that are enhanced by low-Sun photographs. Figure 4-69(a) illustrates the complex of rimless depressions and partially collapsed structures just north of Mare Vaporum and associated with mare sinuous rilles. Figure 4-69(b) shows a sinuous rille crossing a mare arch several times, suggesting that the arch may have formed at a later stage than the rille.

,

EARTHSHINE

PHOTOGRAPHY

Earthshine photography of three regions is illustrated in figure 4-70. Figure 4-70(a) shows the Reiner 7 structure or surface marking seen under earthshine conditions in western Oceanus Procellarum. Figure 4-70(b) shows the crater Schl_iter on the rim of the Orientale basin, and figure 4-70(c) shows the rim and interior of the Orientale basin with Lacus Autumni in the foreground and Lacus Veris in the background.

FIGURE 4-70.-Earthshine photographs. (a) The Reiner 3' area (bright patch, approximately 80 km wide) in western Oceanus Procellarum (AS17-158-23897). Co) The crater Schlater (approximately 90 km in diameter) on the rim of the Orientale basin (AS17-161-24013). (c) View looking southwestward into the Orientale basin with Lacus Autumni in the foreground and Lacus Veris in the background (AS17-158-23901).

The Apollo 17 mission visited the valley of Taurus-Littrow in the mountainous southeastern ring of the great plain of Mare Serenitatis. Between the 1lth and 14th of December, 1972, we conducted 22 hr of surface exploration and experimentation in this valley. Six major geologically defined units within the valley and in the mountains surrounding it (figs. 5-1 and 5-2) were investigated. In the performance of this investigation, we visited 11 major sampling locations, traversed and observed 30 km of the valley floor, collected 97 major rock samples and 75 soil samples, and obtained 2200 documentation photographs. The nearly flawless characteristics of the mission plans and equipment (ref. 5-1), our experience _md training in the geological sciences, and the close cooperation of the science team on Earth provided a much more extensive delineation of the geological context of our investigations than had ever before been possible on the Moon. It now appears that, at Taurus-Littrow, we have looked at and sampled the ancient lunar record ranging backward from the extrusion of old mare basalts 3.7 billion years ago, through the formation of the Mare Serenitatis mountain ring, and thence backward into crystalline materials that may reflect the earliest history of the evolution of the lunar crust itself. Also, materials and processes that range forward from the formation of one of the earliest mare basalt surfaces through 3.7 billion years of modification of that surface have been found and can now be studied. The early portion of this modification included the addition of mantles of glassy spheres that may be the culmination of processes once active within the deep interior of the Moon.

EXPLORATION

PLANS

The photogeology of the valley of Taurus-Littrow and exploration plans based on that geology are described in detail in references 5-2 and 5-3. Figure 5-3 is an Apollo 17 panoramic camera photograph that gives somewhat better detail of the area than was available from the Apollo 15 photographs used for the preflight planning. The stratigraphy and historical sequence of events in the Taurus-Littrow area were largely understood before the Apollo 17 mission (refs. 5-2 and 5-3). This premission sequence, from older to younger events, is summarized as follows. 1. Pre-Serenitatis events included lunar crust development and pre-Serenitatis impact events. 2. The Serenitatis event included formation of the major mountain ring and initial formation of radial grabens such as the Taums-Littrow valley. Uplift of the valley walls may have continued for an extended time after the Serenitatisevent. 3. Ejeeta blankets from the Nectaris and Crisium events probably extended across the Taurus-Littrow area. 4. The Imbrium event, in addition to contributing ejecta to the area, could have accented the formation of grabens like the Taurus-Littrow graben, which is radial to both the Imbrium and Serenitatis basins. 5. Post-Imbrium materials partially Fdled and leveled the valley floor after graben formation was complete or near completion. 6. The Camelot-age cratering events, which were apparently impact events, exposed subfloor material; crater materials are apparently partly mantled by dark material. 7. The Steno-age cratering events consisted of the formation of craters similar to but less subdued than the Camelot-age craters. 5-1

aNASALyndon B. Johnson SpaceCenter.

5-2

APOLLO 17 PRELIMINARY SCIENCE REPORT

FIGURE 5-1.-The majestic valley of Taurus-Littrow, a dark, bay-like identation in the broken mountain chain that defines the edge of Mare Serenitatis. Coordinates of the landing site are latitude 20010' N, longitude 30046' E. The view is northwestward, and the central width of the valley is approximately 7 km (AS17-148-22770).

FIGURE 5-2.-The valley of Taurus-Littrowas seen from the lunar module Challenger on the orbit before powered descent. The command and service module America can be seen crossing the base of the 2301Ym-high South Massif. At its narrowest point between the South and North Massif% valley is 7 km wide. Mare Serenitaiis is the on the horizon (AS17-147-22465).

8. The dark mantle deposition included mantling of older features on a regional scale; the deposits are interpreted as possibly pyroclastic. 9. Effects of the Lee-Lincoln Scarp formation are apparently superposed on North Massif talus; the age relation to the dark mantle material is uncertain, 10. The light mantle deposition was a probable avalanche deposit ofmassifmaterialstransportedover the dark mantle onto the valley floor. 11. The Shorty-age and Van Serg-age cratering events are indicated by small and relatively sharp craters superposed on the younger surfaces of the dark and light mantles, 12. For regolith and talus formation, it is assumed that impact-generated regolith formed on all exposed surfaces as a continuing process throughout lunar history. Talus has similarly accumulated at the base of all steeps lopes, The actual lunar surface traverses (fig. 6-2 of sec. 6) were very close to those planned for the Apollo 17 mission. It was intended to investigate the old, premare materials at the bases of both the South and North Massifs (station 2 and stations 6 and 7, respectively) and possibly at the base of the Sculp-

tured Hills (station 8). Wherever possible, large blocks were to be studied in preference to other features. Materials present beneath the valley floor and the nature of the major craters of the valley were to be studied specifically in the walls and on the rims of several large craters; that is, Emory Crater at station 1 (later moved to a location between the craters Steno and Powell), Camelot Crater at station 5, and Sherlock Crater at station 10 (later eliminated). These large-crater localities and the surface near tile landing point were also intended to be prime areas for investigating the dark floor materials. A concentrated look at the light mantle that extends northeastward from the South Massif was planned for stations 2, 3, and 4. Little work on this problem was possible at station 4; however, a new station on the light mantle (station 2A) was added during the mission. Finally, a study of more recent cratering events, possibly volcanic in origin, was set for station 4 at Shorty Crater and for station 9 at Van Serg Crater. The premission objectives also included extensive plans for sampling lunar soil on the various geologic units. This sampling included collection of samples from the lunar roving vehicle, core-tube samples,

A GEOLOGICAL INVESTIGATION OF THE TAURUS-LITTROW VALLEY

5-3

FIGURE 5-3.-Apollo 17 panoramic camera photograph of the Taurus-Littrow valley with the informal names of various topographic features indicated. The central width of the valley from Nansen Crater to Henson Crater is approximately 7 km (Apollo 17 panoramic camera frame AS17-2309). sample sequences from trenches, samples from special geometric situations, an_ a deep (3.2 m) core sample, All these objectives were met. Several special observational and sampling projects as targets of opportunity were delineated on the basis of the implications of certain lines of interpretation for the origin and nature of various valley features. These special projects were as follows, 1. Coarsely crystalline rock suites associated with the massifs 2. Evidence of fumarolic alteration 3. Evidence of a source or vent of volcanic materials 4. Apparent xenoliths contained within igneous materials 5. Undisturbed glass masses that possibly cooled through the Curie point in situ To greater or lesser degrees, each of these projects received special attention during the Apollo 17 lunar surface explorations. OBSERVATIONAL CONSIDERATIONS

The raw data of our observations during the exploration of the Taurus-Littrow valley exist only in our verbal transcriptions, in videotapes, and in our minds. The synthesis of the data contained in transcripts and videotapes is relatively straightforward and constitutes the foundation of this report. The synthesis of the data contained in the mind is more difficult. Unlike normal field work on Earth, the pressures of time and total efficiency on the Moon prevent the conscious mental recording of visual images. Many images are recorded, to be sure, but some are not subject to direct recall. Not only may an

5-4

APOLLO 17 PRELIMINARY SCIENCE REPORT The North Massif

external stimulus, such as a photograph or a question, be required to release these data, but there is a continued problem, which worsens as time passes, of separating purely objective observational data from more subjective feelings acquired since the mission. In recognition of this problem, the transcripts and tapes have been used extensively for verification of observations. Possible interpretive explanations and alternarives are observational the environment ofin the Tauruslast section this paper, The included in Littrow valley is superb. Unfiltered sunlight is an

The North and South Massifs form the majestic walls of the Taurus-Littrow valley and rise to heights of 2000 and 2300 m, respectively, above the valley floor, with flanking slopes of approximately 25 ° . The massifs represent the major structural boundaries of the valley. Their faces contain intermittent exposures of thick sections of premare crustal rocks. Numerous fields, or "source-crops," of boulders are present on the upper one-half to two-thirds of the slopes of both massifs. Boulder tracks indicate that blocks have rolled into the valley from these sources. Several of these blocks were the prime field objectives of our traverses in the Taurus-Littrow valley. The source-crops for the boulders on the slopes of the North Massif are linear but discontinuous. They are roughly horizontal in apparent orientation, and each is a few hundred meters in length. The large boulder investigated at station 6 (fig. 5-4) has a well-defmed track above it and appears to have originated from the lowermost source-crop band approximately one-third of the way up the slope. Based on what had been seen on previous lunar missions, the geologic complexity of the boulders at stations 6 and 7 was unexpected. Here, for the first time, it was possible to observe and sample across a major lithologic and structural contact. This contact was exposed sharply in boulders large enough that outcrop investigative techniques could be applied. As always, however, time was relentless and many

excellent light for visual investigation. When this light is combined with generally clean rock surfaces, there is little difficulty in distinguishing mineralogical and textural differences. Albedo and textural differences in soil and rock surfaces also are readily apparent. For the most part, the sampling of rocks and soils was based on visually detectable differences or similarities. These characteristics were recognizable despite an overall brownish patina on most rock surfaces. Unfortunately, of the more human eye. NOMENCLATURE In this report, consistency with our field (transcript) terminology has been maintained except in a few instances. The term "anorthositic gabbro" has been dropped in favor of "tan-gray mattix-rich breccia." The term "blue-gray breccia" has been subdivided into "blue-gray matrix-rich breccia" and "blue-gray fragment-rich breccia." Finally, the term "dark mantle" has been replaced by "dark floor material" because a mantling origin is subject to question at the time of preparation of this report. In most cases, breccias are distinguished as "matrix-rich" or "fragment-rich" depending on which textural component is visually dominant in a given boulder. For correlation of the field terms used in this section with those used in section 6 of this report, see table 6-III. FIELD OBSERVATIONS photographs cannot yet record to the much subtle information available

The general historical or stratigraphic sequence of major geologic units in the Taurus-Littrow region was well understood before our investigations on the surface. What remained to be done was the correlation of the detailed field stratigraphic sequences with this general regional sequence. The field observations are discussed in detail in the following paragraphs,

FIGURE 5-4.-View looking south from station 6 on the North Massif and including the large boutders of bluegray breccia (left) and tan-gray breccia (right) sampled at this locality (AS17-140-21496).

A GEOLOGICAL INVESTIGATION OF THE TAURUS-LITTROW VALLEY questions were only partially answered. Still, much was learned, Three major categories of stratigraphic materials were studied and sampled in the boulders at stations 6 and 7. A younger, freely crystalline, strikingly vesicular, tan-gray, matrix-rich breccia (fig. 5-5) is apparently in intrusive contact with an older, very finely crystalline, blue-gray, fragment-rich breccia (fig. 5-6). There are inclusions of blue-gray breccia in the tan-gray breccia at the contact in the station 6 boulder. A blue-gray matrix-rich breccia is the material in direct contact with the tan-gray breccia in both the contacts investigated. This blue-gray matrix-rich breccia forms a contact zone approximately 1 m wide, apparently produced from the blue-gray [ragment-rich breccia in the boulder at station 6. The large vesicles in the tan-gray breccia are ellipsoidal in cross section and are generally alined parallel to the contact with the blue-gray breccia. There were some small vesicles in the blue-gray breccia near this contact in the boulder at station 6. In addition to the common small blue-gray fragments that dominate the blue-gray fragment-rich breccia, there are distinctive clasts of hght-gray breccias. Within the contact zone at station 7, one of these clasts i_ ueined by blue-gray matrix-rich breccia

5-5

(fig. 5-7). The clasts also appear deformed and partially mixed with blue-gray material in the station 6 boulders. The distinctive clasts are apparently the oldest stratigraphic materials sampled at the TaurusLittrow site. Scattered, distinctive, light-colored clasts also are present in the tan-gray breccia; however, the stratigraphic relations of these clasts to either the blue-gray breccia or its included clasts were not apparent. A marked brown patina is well developed on all weathered rock surfaces in the Taurus-Littrow valley. The patina is most prominent on the surfaces of the massif breccias, including the fractured surfaces of the blocks with well-preserved boulder tracks above them at station 6. The light-gray walls of craters on the slopes of the North Massif and light-gray material we uncovered with our boots suggest that this type of fine debris, mixed with boulders, forms the bulk of the talus at the base of the massif. Fillets of this material are largely absent around boulders except on some uphill sides. Overlying the light-gray fine-grained talus is a medinm-gray surface material that is generally a few centimeters thick. Unlike the Filleted boulders of the

FIGURE 5-5.-Vesicular, tan-gray, matrix-rich breccia at station 6. Note the scattered distinctive light-colored clasts and the general alinement of vesiclestrending from lower left to upper right. The horizontal width of the illuminated portion of the boulder is approximately 1.5 m (AS17-140-21423).

FIGURE 5-6.-The large boulder investigated at station 7 on the North Massif.The boulder is approximately 2 m wide and contains a sharp contact between vesicular tan-gray breccia on the left and blue-graybreccia on the right. A tabular distinctive clast is present on the extremeright, and a weathering patina is indicated by light areas where sampleswere taken (AS17-146-22336).

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APOLLO 17 PRELIMINARY SCIENCE REPORT

FIGURE 5-7.-Vein of blue-graymatrix-rich breccia cutting a distinctive clast of anorthositic matrix-rich breccia in the boulder at station 7. The vein is continuous with the major mass of blue-graymatrix-rich breccia that encloses the clast. The width of the angled end of the tongs is 6 cm (AS17-146-22327). valley floor, the sides of boulders commonly hang this surface material. over-

FIGURE 5-8.-Southwest-looking view of the 2300-m-high South Massifas seen from station 6 at the base of the North Massif. Station 2 is located near the center of the photograph and is approximately 10 km away. Southeastto northwest-plunging albedo lineaments suggest the attitude of internal massif structure. North Massif talus debris is in the foreground (AS17-140-21491).

ward the west. Offsets of the color changes, downward to the east, suggest that normal faults dipping steeply eastward cut the massif structure. The boulders investigated at station 2 (fig. 5-9) included crystalline, tan-gray matrix-rich breccia and blue-gray matrix-rich breccia, but no contact relations were observed. The tan-gray breccia is less vesicular and more heterogeneous in texture than its North Massif counterpart. The sampled blue-gray breccia is similar to that found in the contact zones of the North Massif boulders. From a distance, boulders of both these rock types have a tan-gray hue very similar to that of the materials below the blue-gray tones in the high portions of the South Massif. The distinctive clasts of contrasting shades and hues in the tan-gray and blue-gray breccias of the South Massif generally appear similar to those in the North Massif breccias. However, one crystalline clast in the boulder of blue-gray matrix-rich breccia has proved to be composed largely of olivine (sec. 7). The preliminary examination of rocks from both the South and North Massifs also suggests that various crystalline mafic rocks and some ultramafic rocks make up a significant portion of the distinctive clast population. The third boulder examined at station 2 was a strongly foliated and layered fragment-rich breccia

The South Massif The rocks of the South Massif (fig. 5-8) constituted the prime geological objective on the mission to the Taurus-Littrow valley, although the long traverse to the South Massif clearly taxed the operational limits of our surface exploration capabilities. An hour-long trip to the edge of Nansen Crater at the base of the massif, for approximately 60 min of exploration time there, meant that the remainder of this excursion would be extremely limited in time available for exploration. The boulders that were our specific objectives held the promise of an unparalleled view into the history of the lunar crust. Although overshadowed by more spectacular later discoveries, we were not to be disappointed by "old station 2." The most obvious sources for the boulders near station 2 are on the upper one-fourth of the South Massif slope. Visual inspection from a distance indicared that linear source-crops on this part of the massif and subtle linear color variations of blue-gray lying over tan-gray have an apparent dip of 10 ° to 15 ° to-

A GEOLOGICAL INVESTIGATION OF THE TAURUS-LITTROW VALLEY

5-7

_ _ 45

FIGURE 5-9.-View looking southwest and encompassingthe boulders investigated at station 2. The boulders lie along the base of the South Massiftalus slope. The surface of the light mantle is in the foreground. The lunar roving vehicleis 183 cm wide (AS17-138-21072). FIGURE 5-10.-Foliated and layered_breccia investigated at station 2. Four sampleswere obtained across the layering, which trends from the upper left to the lower right in the photograph. The visible portion of the gnomon rod is approximately 45 cm long (AS17-137-20903).

(fig. 5-10) that is much less coherent than either the tan-gray or blue-gray breccia types. This foliated and layered breccia contains large clasts of both dark- and light-colored older breccias in a generally lightcolored matrix. There are also small clasts with distinctive dark coronas around them. From a distance, this boulder has a blue-gray hue very similar to that of the blue-gray materials observed :near the top of the western portion of the South Massif. Along the boundary between the South Massif and the valley floor, there is a trough. This trough is much broader and more continuous than had been apparent before the mission. The trough is a few hundred meters wide at station 2, is flat floored, and seems to include the crater Nansen as an integral, although much deeper, topographic unit. The observed properties of the tahis material at the base of the South Massif are very similar to those observed at the North Massif. In Nansen Crater, it is also clear that at least some of the South Massif talus forms a younger toe of debris over the valley floor, particularly over the light mantle deposits present in Nansen (fig. 5-11).

FIGURE 5-11.-View from near station 2, looking northwest into the crater Nansen and along the contact between the South Massiftalus and the light mantle. Note the lobe of talus debris lying on the light mantle in Nansen. The boulders are on the order of 3 to 5 m in diameter (AS17-138-21058).

5-8

APOLLO 17 PRELIMINARY SCIENCE REPORT The Sculptured Hills fragment was unfilleted and projected only a few centimeters into the underlying soil. Other exotic white fragments in small secondary craters appeared to be anorthositic matrix-rich breccias (fig. 5-13). The soil on the slope material at station 8 has a uniform grain size and is medium to dark gray in color in a trench dug to a depth of 30 cm (fig. 5-14). In this regard, the slope materials of the Sculptured Hills resemble the soils on the dark floor material in the valley rather than those on the massifs or on the light mantle. The Valley Floor

The interlocking domes of the Sculptured Hills form the northeastern wall of the Taurus-Littrow valley. The origin of this unusual physiographic unit remains unknown, although some relation to the processes associated with the Serenltatis impact event is indicated by morphologically similar units near other large lunar basins (ref. 5-2). Our investigation at station 8 on the lower slopes of the the nature of Hills gave no definitive evidence about Sculptured bedrock units. Concentrations of boulders were observed only near the tops of the hills, and no boulder tracks were apparent above the few blocks visible on the lower slopes (fig. 5-12). The surface texture much finer scale and is more wrinkled tured Hills is of of the slope material on the Sculpin appearance than that of comparably lighted slopes on the massifs, Of the six blocks examined in the vicinity of station 8, five were composed of crystalline basalt similar to that in the Camelot-Steno area. The sixth block was a black, glass-coated, coarsely crystalline rock made up of approximately equal parts of a yellowish mafic mineral and white to bluish-gray plagioclase and maskelynite. This apparently exotic

The dark floor of the Taurus-Littrow valley is underlain by a body of basalt between the bounding massifs. Since formation, this material has been subjected to a variety of cratering, depositional, structural, and possibly volcanic processes. In addition to the investigation of block fields in the valley, our goals included the study of the Camelot- and Steno-age cratering events, the depositional characteristics of the dark floor material, the structural history of the valley floor, and any volcanic features we might encounter.

FIGURE 5-12.-View from station 8 looking northeast up the slope of the Sculptured Hills. Note the small number of boulders relative to the talus deposits around the massifs.The boulder in the distant center of the photograph is approximately 0.5 m in diameter (AS17-14221734).

FIGURE 5-13.-Secondary crater approximately 1 m in diameter in the wall of a larger crater near station 8. The central portion of the secondary crater contains several fragments of white, anorthositic, matrix-rich breccia that appears to have been part of the crater-formingprojectile (AS17-146-22399).

A GEOLOGICAL INVESTIGATION OF THE TAURUS-LITTROW VALLEY The block fields concentrated near and in the large craters in the Camelot-Steno area allowed a rather comprehensive investigation of the basalts. The blocks are largely massive, tan to pinkish-gray, coarse-grained, ilmenite basalts generally having a coarsely vesicular texture. Isolated examples of eggsized vesicles were observed near the crater Bronte. Locally, there is a strong foliation formed by the occurrence of parallel parting planes or f_actures (fig. 5-15). The blocks on the rim of Camelot Crater at station 5 showed parallel layers defined by differences in vesicle concentrations. Only two fragments of aphanitic basalt were observed despite a search for this variety at each sampling site. Both fragments were finely porphyritic, and the one from the crater Shorty was 'very coarsely vesicular. Other fine-grained to aphanitic basalt fragments are present in the suites of sm_dl fragments collected in rake and soil samples (sec. 7). In some blocks, finely textured blue-gray basalt forms isolated irregular lenses within the tan-gray coarse-grained basalt (fig. 5-16). Material of a similar blue-gray color was seen from a distance in the western wall of the crater Cochise, where it forms a unit several tens of meters thick over a tan-gray unit (fig. 5-17). The contact has an apparent dip of

5-9

FIGURE 5-15.-Basalt block at station 5 on the southern rim of Camelot Crater showingfoliation causedby the35.5 cm orientation of vesicle concentrations. Hammer is parallel long (AS17-145-22153).

FIGURE 5-14.-The trench wall in soil at station 8 on the slope of the Sculptured Hills. Note the lack of apparent structure within the soil. The color scale on the gnomon leg is 15 cm long (AS17-142-21720).

APOLLO 17 PRELIMINARY SCIENCE REPORT The regolith on dark floor material consists of loose, f'me, sedate debris with few fragments larger than approximately 1 cm (fig. 5-18). The regolith is a sparkling dark gray at the surface with even darker gray material just below the surface, at least in the optically lightened area near the lunar module (fig. 5-19). Locally, the fragment populations on the dark floor material are quite variable. In the general vicinity of the Steno-class craters that form the cluster of craters south of the landing point, the fragment frequency is higher b) a factor of 4 or 5 than it is near the Camelot-class craters or in areas along the traverse west of Camelot Crater and near the crater Shakespeare. Although coherent soft breccias were sought in this general area, none were recognized; however, a few examples were collected (see. 7) inadvertently as a consequence of attempts to sample fine-grained basaltic materials. The dark floor material has many field characteristics that suggest it is a mantling deposit, as do its characteristics as seen from orbit and in orbital photographs (ref. 5-4 and part B of sec. 29). The field characteristics are as follows. 1. The block fields associated with large craters

FIGURE 5-17.-View from the Note the medium-_aycrater Coehise looking northwest. southern rim of the unit lying over the light-gray unit in the western wall of the crater. The apparent dip of the contact between the two units is to the north. The units are tentatively interpreted to be varieties of basalt based on visual similarities to other basalts investigatedin detail (AS17-146-22411). approximately 20 ° to the north. The units in Coctrise Crater could be the two varieties of subfloor basalt. In general, however, the tan-gray coarsely vesicular variety of subfloor basalt is dominant (at least 95 percent) in the basaltic block fields along our traverses. A general absence of obvious shock effects was noted in the blocks of basalt studied in the field. Other than the pervasively fractured basalt block at Shorty Crater and possibly the very-fine-grained mylonitic zones along isolated fractures in other blocks, the basalts seemed to have been only slightly metamorphosed by the formation of large craters in the valley. Despite the paucity of shock effects, the morphology of the large craters is consistent with their being impact craters of at least two general age groups that have been subsequently modified by the deposition of the dark floor material. The floor of the valley is largely covered with this dark material. Below the dark floor surface, there are probably interlayered ejecta blankets from the variOUS large craters. Boulders in these ejecta blankets project above the surface in the lunar module and Steno Crater areas,

FIGURE 5-18.-View from the lunar module (LM) landing site looking north across dark floor material toward the North Massif.The surfacerelativeforeground is typical of the dark floor material in the to the abundance of craters and basalt fragments.The small crater just right of center in the photograph is approximately 3 m in diameter (AS17-136-20693).

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5-11

FIGURE 5-19.-View from LM window looking west toward Family Mountain. The ALSEP site is at the center of the photograph. Note that the local area around the LM has a higher albedo than that of more distant areasof the valley or of the disturbed dark floor material nearby. The mechanical effect of the descent engine effluents appears to have caused a change in the albedo of the immediate surface near the landing point (AS17140-21355). are largely confined to the inner walls of the craters (fig. 5-20). The rims of these craters are generally covered by dark floor material for distances of 20 to 30 m down the crater wall from the tim. Locally, the block fields of the crater walls extend up to, but rarely over, the rim crest (fig. 5-21). In these few places, the edge of the block field terminates sharply against the dark floor material outside the crater. No differences were observed between dark: floor material on or away from crater rims. 2. Dark floor material locally extends walls in long downward-pointing fans that bury the wall block fields. The crater universally covered by the same material. 3. Dark floor material constitutes the over crater apparently floors are interblock

FIGURE 5-20.-View from station 5 looking north acrossthe crater Camelot and toward the North Massif. Note both the concentration of blocks on the inner wallof the crater and the dark floor material that generally covers the crater rim. The crater is approximately 600 m in diameter, and the North Massifrises approximately 2200 m above the valley floor (AS17-145-22181).

material in all block fields (fig. 5-22). If the large blocks of the block fields are assumed to be generally equidimensional in shape, then they are approximately half buried in the dark floor material that surrounds each individual block. However, no dark floor material distinctly mantles the top of any block, 4. All observed craters in dark floor material that are between approximately 5 and 80 m in diameter have dark floor material on their ejecta blankets, rims, walls, and floors. However, there is no indication of extensive filling of such craters. "Van Serg was the only observed crater that had a clearly defined blocky rim. Fresh craters less than 5 m in diameter

FIGURE 5-21.-View from station 5 looking east along the southern rim of the crater Camelot. Note the relatively sharp contrast between the basalt block fields and the dark floor material that covers the crater rim. The wheelbase of the lunar roving vehicle is 229 cm (AS17145-22162). have coverings of weakly coherent soil breccia fragments. 5. As will be detailed later, the orange and black

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APOLLO 17 PRELIMINARY SCIENCE REPORT

FIGURE 5-22.-View looking west from station 5 on the southern rim of Camelot Crater. The photograph shows the general slope and distribution of basalt blocks on the rim and inner walls of the crater. The large block just right of center is approximately 2 m high (AS17-14522174).

glasses at Shorty Crater partially mantle that crater. These glasses have affinities with the fine-gained fractions of the dark floor material (sec. 7). Boulder surfaces are generally free of dust except in depressions on horizontal rock surfaces where dust and relatively coarse rock and mineral debris have accumulated (fig. 5-23). Fillets tend to be low on boulders on the valley floor, although isolated exceptions to this rule were observed, particularly near the ApoUo lunar surface experiments package (ALSEP) deployment site. The visually apparent saturation crater size on the dark floor material is probably approximately 0.5 m, which suggests a 10-cm-deep gardened zone. Mechanical penetrability decreased markedly below approximately 10 to 15 cm, and hand penetration with a core tube was impossible below approximately 25 cm under the lunar module, The Light Mantle Area The plume- or ray-shaped light-albedo area that extends northward from the South Massif is known as the light mantle. Photogeologic interpretation suggested that this was a relatively young mantling material derived from the South Massif talus (ref. 5-3). The geometry of its contact and the dark material excavated by some of the larger craters on it strongly suggest that the light mantle deposition occurred after most of the dark floor material had been deposited. Whether this light mantle material was a ray of ejecta or mobilized South Massif talus or

FIGURE 5-23.-Regolithic debris partly filling cracks and depressions on a large basalt block at station 5. Note relative lack of debris on flat and more exposed surfaces of the block. The gray scale on the gnomon is 30 cm long (AS17-145-22155).

both and speculation on the possible mechanisms of deposition were questions posed in our premission planning. The surface of the light mantle is composed of loose, medium-gray, finely seriate debris with an apparently large deficiency of fragments in size ranges greater than approximately 1 cm (fig. 5-24). Very few rock fragments or boulders larger than a few centimeters were observed; this characteristic contrasts sharply with the talus debris on the South Massif. The fight mantle surface was very similar in general visual character, however, to the fine debris surface on the South Massif talus slope. Fragments of breccia similar to those at station 2 were found slightly concentrated on the rim of and inside the 30-m-diameter Ballet Crater in the light mantle at station 3 (fig. 5-25). In general, fragment concentrations were present on the rims and in the walls of craters having diameters greater than approximately 5 m. A dilated and inverted section of the light mantle may be present in the fine-grained debris just outside the rim of Ballet Crater. A trench in this rim (fig. 5-26) showed the debris to be layered from the surface downward as follows. 1. Approximately 0.5 cm of medium-gray surface

A GEOLOGICAL

INVESTIGATION

OF THE TAURUS-LITTROW

VALLEY

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FIGURE 5-24.-View from the Roman Steppe looking northeast toward Wessex Cleft. Station 2A on the light mantle is in the general area of the center of the photograph. Note the low abundance of fragments on the surface of the light mantle (AS17-138-21095).

FIGURE 5-26.-The fine structure of the ejecta on the rim of Ballet Crater at station 3. This trench exposed the first such structure observed in situ on the Moon. The visible portion of the gnomon rod is approximately 40 cm long (AS17-138-21148).

_ .... : ....

material (possibly new regolith) similar to the surface layer on the light mantle 2. Approximately 3 cm of light-gray material similar to the subsurface material of the light mantle 3. At least 15 cm of mediumto dark-gray material into which light-gray material is marbled The talus slopes of the massifs clearly have a higher rock fragment abundance than does the average surface of the dark floor material; however, the surface of the light mantle has a distinctly lower fragment abundance in the 2- to 10-cm size range. The same relations hold for fragments larger than 10 cm. Observations of crater characteristics infer that concentrations approximately mantle. of rock fragments 1 m below the occur surface at depths of of the light

......

......... FIGURE 5-25.-Ballet Crater at station 3 looking north along the Lee-Lincoln Scarp. The crater is approximately 30 m in diameter and is typical of craters of this general size in the light mantle that expose fragments of buried breccia, The scoop handle is 76 cm long (AS17-138-21160).

Light-gray material is present 5 to 10 cm below the medium-gray surface material at all localities investigated in the light mantle area. Light-gray material is also present in the walls of all craters in this area having diameters greater than approximately 1 m. This soil prof'de is very similar to that developed on the massif talus slopes. The contacts between the light mantle and both

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APOLLO 17 PRELIMINARY SCIENCE REPORT tend to be oriented with their long axes radial to the center of the crater. 3. There is a central pit in an otherwise relatively flat floor. The diameter of the pit is approximately one-fourth to one-fifth the rim diameter of the crater. The pit is generally shallow, in most cases less than one-tenth the depth of the crater. However, this depth does vary; in one instance, the pit was nearly one-half the depth of the crater and roughly cylindrical in shape. 4. The central pit is glass lined with the glass forming a coating and partially cementing the soil breccia fragments. 5. The relative geometry of the pit with respect to the crater appears to be constant and independent of crater size or of geologic unit. 6. Overall, the albedo of the crater and its ejecta is slightly higher than that of its surroundings. As the crater ages, the order of the disappearance of primary features is, first, the albedo contrast, then the glass in the central pit, then the soil breccias, and, f'mally, the central pit itself. Shorty Crater One of the premission alternatives around which our exploration was planned was the possibility that the 110-m-diameter crater Shorty was a volcanic vent. Although its general morphological appearance is that of a dark-rayed impact crater that had penetrated the light mantle, Shorty Crater held out the possibility of young volcanism. Other than Shorty, possible sources for the potential pyroclastic deposits of the dark floor material were difficult to delineate. The observations and sampling at Shorty Crater did not reveal directly what we had expected; however, the results of the investigation may yield equally important information from unexpected directions. All the now classic difficulties in conducting geological operations on the surface of the Moon faced us at Shorty Crater. To begin with, we had made earlier decisions to spend extra time at previous localities without knowing what awaited us. Our oxygen supply limited the time we could spend at Shorty Crater to a clearly nonnegotiable 35 min. The normal "housekeeping" duties of dusting and reading the gravimeter demanded their usual but necessary due. Then, in addition to the usual complexities of lunar impact appeared. geology, an unexpected discovery

the dark floor material of the valley and the dark material around Shorty Crater are gradational in albedo over a distance of approximately 10 m. A distinct difference in albedo of the two types of surfaces is visible when viewed at zero-phase angle, Also, there is an obvious change in the wall color of craters larger than 1 m in diameter. No topographic expression at these contacts was detected, The light mantle surfaces above, on, or below the Lee-Lincoln Scarp show no discernible differences in crater population, fragment population, or surface texture, Craters smaller than approximately 5 m in diameter were found to have a consistent morphology whether in light mantle, dark floor material, or massif talus (fig. 5-27). In summary, the freshest of these craters have the following characteristics. 1. The crater ejecta, rim, wall, and floor are covered with fragments of weakly coherent soil breccia as large as 10 to 15 cm in average diameter, The albedo of these soil breccias is much higher in the light mantle than on the dark floor material, 2. The soil breccia fragments inside the crater

FIGURE 5-27.-View from between the LMand ALSEPsites looking east toward the LM. A portion of a fresh, 3-m-diameter crater is in the foreground. The glassy central center thisthe crater. Note the more reflective area in the pit of of crater is the slightly abundance of small fragments of soil breccia in and around the crater (AS17-145-22185).

A GEOLOGICAL INVESTIGATION OF THE TAURUS-LITTROW VALLEY Shorty Crater has features consistent with an impact origin, although no one feature is conclusive in itself. Subfloor basalt appears to dominate the few blocks at the rim (fig. 5-28). One of these blocks is pervasively fractured and may be shocked. The crater waU is locally blocky and has several radial and transverse changes in texture and albedo. There is no continuous bench in the crater wall; however, several well-defined lobes of coarse and fine debris, similar to those in the walls, extend out onto the floor and may be the relics of such a bench (fig. 5-29). The blocky materials on the flat floor appeared to be highly fractured but otherwise uniform in texture. Parallel fracture organization is strong in some blocks. The unexpected discovery at Shorty Crater was the presence of at least three deposits of very-finegrained orange soil (fig. 5-30). There were also numerous indications of fine-grained black soil, which, together with the orange soil, was subsequently determined to be composed almost entirely of glass beads or devitrified glass beads of uniform composition (sec. 7). Two of the orange soil deposits are near the rim crest of the crater, whereas the other deposit is exposed on the western wall. In appearance, the deposits have many of the characteristics of fumarolic alteration halos; with this hope, we conducted our observation and sampling activities. One deposit of orange soil was trenched across its trend along the crater rim. At this location, it was

5-15

_'_

FIGURE 5-29.-View of the northwestern wall of Shorty Crater. The diameter of the crater is approximately 110 m. Note the dark band on the far wall (AS17-137-20995).

FIGURE 5-28.-The southern rim of Shorty Crater looking west. The sampled orange soil deposit is at the left center of the photograph near the large boulder. Note the heterogeneity of boulder and albedo distribution patterns. The crater is approximately 110 m in diameter (AS17137-21009).

FIGURE 5-30.-Near-surface cross section of the startling deposit of orange soil on the southern rim of Shorty Crater. The pervasivelyfractured rock in the background is coarse-grained basalt. The gnomon rod is 46 cm long (AS17-137-20990).

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APOLLO 17 PRELIMINARY SCIENCE REPORT

sampled in detail and the following relationships were observed. 1. The deposit is approximately 1 by 4 m in size at the surface and is elongate parallel to the rim crest. 2. The deposit has no topographic relief relative to other rim surfaces. (This is also true for the other rim deposit.) 3. Dark-gray surface material forms an approximately 0.5-cm-thick surface layer over both the deposit and the surrounding light-gray materials. There is an orange tint to this surface material directly over the deposit. 4. The contact of the deposit with light-gray debris on either side is irregular in detail but essentially vertical to a depth of at least 20 cm. 5. From the vertical contacts inward, the deposit grades from a yellowish orange over a distance of approximately 10 or 15 cm to a reddish orange. 6. The reddish-orange inner portion of the deposit is moderately coherent and is crossed by at least two apparent joint sets. 7. from that from 8. During the postmission unpacking of a sample the reddish-orange zone, a clod was observed was sharply and concentrically zoned inward orange brown-gray to bluish gray. Examinations of the outer surface of the core

FIGURE 5-31.-View of the northwestern wall of Van Serg Crater. The diameter of the crater is approximately 90 m. The dark fans on the inner wall terminate at the top of a nearly continuous bench. The upper portion of the gnomon rod is approximately 30.5 cm long (AS17-14622429).

tube drawn from the deposit showed that the orange glass changes sharply to a black material at a depth of approximately 25 cm. The black material extends to a depth of at least 70 cm. One can conceive of many samples and observations left uncollected at this remarkable locality, However, few of our experiences in the Apollo Program better illustrate the inherent quality of scientific investigation that is possible from the integrated effort of so many in so short a time. Van Set9 Crater Premission photogeologic studies suggested that the relatively fresh appearing 90-m-diameter crater Van Serg would provide an impact-generated sample of the section of units lying above the basalts of the valley. Located just south of the craters Cochise and Shakespeare, Van Serg Crater might also penetrate and sample ejecta from these much older craters. As at Shorty Crater, the unexpected again was encountered. All features of Van Serg Crater were consistent with an impact origin (fig. 5-31). However, unex-

pected, dark, matrix-rich, regolithic breccias were found to be the dominant rock type on the blocky rim and the equally blocky ejecta blanket. Such breccias had not been observed elsewhere in the valley. A few of the Van Serg breccias are intensely fractured and very friable, and others are mixed or covered with black glass. No basalt was observed, although one fragment was obtained as a glass-coated grab sample. A dark surface cover a few centimeters thick exists over light-gray debris in some of the interblock areas and may cover all the ejecta blanket and rim. The dark cover may be the disintegration product of the dark breccias or, alternatively, it may be a separate mantle. Most blocks are partially embedded in this material. The crater wall is very blocky and is interrupted by a nearly continuous bench approximately halfway down into the crater. Rocks below the bench are slightly darker in color than those above. Dark fans of dark-gray debris locally cross over the rim and down the upper wall but generally terminate at the bench. The crater floor is also very blocky with some intense

A GEOLOGICAL INVESTIGATION OF THE TAURUS-LITTROW VALLEY shattering of blocks, although, in contrast to Shorty Crater, the blocks are much larger. Some of tire floor blocks are coarse, blue-gray, fragment-rich breccias with light-colored clasts as large as 1 m in diameter, The general nature of the floor breccias of Van Serg Crater and the visual observation of a thick, northward-dipping, blue-gray unit above the subfloor basalt in the northern wall of Cochise the possibility of a major new breccia portion of the valley. The possible structural implications of such a unit clear, SPECIAL F EATU R ES Crater opens unit in this origins and are not yet

5-17

coarse mottled texture that shows a roughly horizontal lineation on near-vertical surfaces. The elongate light-colored areas that cause the mottling are approximately 1 by 2 cm in size. The origin of this mottling and its llneation was not apparent in the field but may be related to the impact geometry of secondary particles. Boulder Tracks

Among the most striking and potentially most useful features of the massifs are the boulder tracks leading from source-crops high on the slopes to large boulders near their bases (fig. 5-32). It appears that once a boulder is jarred loose and begins to roll, only a decrease in slope or the disintegration of the boulder will stop it. The tracks are made up of chains of small depressions. These chains are generally straight; however, gradual curves were noted in some instances. Not all tracks are exactly perpendicular to the contours, and, in some cases, the tracks curve noticeably. Most boulders stopped rolling at least a few tens of meters before reaching the base of the massif slope. However, two large boulders in the crater Nansen moved across the base of the slope and up the other side of the crater for several tens of meters.

A number of special features were examined and sampled during our general investigation of the Taurus-Littrow valley. These features are only periphorally related to the general stratigraphy of the area and are discussed separately in the following paragraphs. Rock Fragment Weathering In all instances except for Van Serg Crater and the small pit-bottomed craters, the rock fragments around and in craters on the dark floor surface are the very coherent subfloor basalts. The fragments associated with craters in the light mantle are the similarly coherent tan-gray and blue-gray breccias. In contrast, the Van Serg-type dark matrix-rich breccias and the soil breccias in the pit-bottomed craters appear to have limited durability in the valley environment. The gross shape of coherent rock fragments is angular. Edges and corners are rounded except where recent impact fracturing has occurred. The gross shape of pervasively fractured and friable rock fragments also tends to be angular, but, in these cases, the edges and corners are also angular. The only generally rounded rock fragments observed were the unfractured dark matrLx-rich breccias at Van Serg Crater. The weathered surfaces of all subfloor basalts, except for the aphanitic group, are lighter colored than are the fresh surfaces. The lighter color appears to be due to the surficial shattering of feldspar in microcraters. This observation is generally true but to a lesser degree for the very finely crystalline breccias of the massifs. Glass linings in microcraters are more common on these breccia surfaces than they are on the basalt surfaces, The coarse-grained subfloor basalts also have a

FIGURE 5-32.-A 500-mmqens photograph of boulders and boulder tracks on the slopes of the North Massif.The largest boulders are on the order of 5 m in diameter (As17-144-21991).

5-18 The Lee-Lincoln Littte new information

APOLLO 17 PRELIMINARY SCIENCE REPORT Scarp was obtained on the

Lee-Lincoln Scarp (fig. 5-33) through our surface observations. There is no surface expression of the scarp other than the topography, which was well known before the mission. The east-west trending lobes that characterize the scarp on the valley floor were particularly impressive. No indication of rocky bedrock was seen on any portion of the scarp, although large blocks are present on the northwestern wall of Lara Crater. The most striking new observation was the change in surface texture across the Jefferson portion of the scarp on the North Massif. The lineations apparent on the North Massif are not present on the surface south and southwest of the scarp. Also, fewer craters are apparent on the southern and southwestern side. This less-textured surface appears to be continuous across the break in slope at the base of the North Massif.

Soil Sampling The soils of the Moon are the prime historical record of the lunar surface environment and of the solar and cosmic environment of near-Earth space. The presence of the massifs, of boulder overhangs, of the Lee-Lincoln Scarp, and of a number of different stratigraphic surfaces made possible the collection of a wide variety of soil samples in the valley of Taurus-Littrow. In addition, at most documentedsample localities, a standardized 0.5- to 1-cm-thick skim sample of the local surface was obtained, followed by a sample of the underlying soil to a depth of approximately 5 cm. Also, most rock samples were bagged with a small amount of soil. A new sampling device for sampling from the lunar roving vehicle permitted a substantial increase in statistical control of soil variations between stations. This device also made possible a broader sampling of the lunar module area in the course of other activities, Soil samples for volatile migration studies, such as in east-west split boulder (or boulder-massif) situations, and from permanently shadowed overhangs were obtained at both the North and South Massif study sites. Samples in the center of and outside a boulder track were taken on the North Massif. Also, samples from underneath boulders were obtained at the South Massif and Sculptured Hills sites,

FIGURE 5-33.-View from near Hole-in-the-Walllooking north along the Lee-Lincoln Scarp and showing the Jefferson Scarp along the side of the North Massif. station 3 is in the left foreground on the slope of the scarp. The scarp rises approximately 80 m above the surface of the valley, here covered by the light mantle (AS17-138-21118). The possibility of increased volatile activity along the Lee-Lincoln Scarp was used to establish the site for a vacuum-sealed core-tube sample taken at a depth of 35 to 70 cm in soil on the scarp at station 3. Core-tube samples also were obtained in the softs of all major geologic units and in the orange/black glass deposit at Shorty Crater. In addition to the vertical soil profiles sampled by the core tubes, trench profiles were sampled in the rim of Ballet Crater, in the slope material at the base of the Sculptured Hills, and in the ejecta blanket of Van Serg Crater. Finally, to aid in examining the recent magnetic field of the valley, two agglutinated glass and soil breccia samples were obtained, one from the pit in a fresh crater west of the lunar module and the other from a glassy mass on the rim of Van Serg Crater. These glasses appeared to have been undisturbed since they cooled in situ. The Regolith It appears that regolith development on the massif talus materials and on the light mantle is indicated by

A GEOLOGICAL INVESTIGATION OF THE TAURUS-LITTROW VALLEY the average depth of medium-gray soil above the lighter gray material. The depth of this regolith is on the order of 5 to 10 cm. The regolith on the dark floor material is more difficult to define visually. In the vicinity of the lunar module, the loose or very weakly colherent debris appears to be approximately 15 to 20 cm deep. This depth is roughly consistent with what appeared to be an approximately 0.5- to 1-m-diameter saturation crater size for the surface, which suggests that the age of the dark floor surface is only two or three times that of the light mantle surface or of the present talus surfaces, Both the dark floor material and the light mantle have intercrater surfaces covered by the "raindrop" pattern of small craters. This pattern appears better defmed and finer in scale on the light mantle than on the dark floor surface. No systematic linear structures were visible on either the light mantle ,;urface or the dark floor surface. Such structure was apparent on the steep slopes of the massifs and the Sculptured Hills; however, these slopes are better analyzed photographically than visually, STRATIG It is yet RAPHIC SUMMARY to come to any final

5-19

produced during the formation of the large lunar basins or even older events.) 3. Crystalline, tan-gray, matrix-rich breccia and any metamorphic effects associated with its intrusion into the blue-gray breccias. (These intrusions may be partially molten impact breccias, possibly of Serenitatis age, or polygenetic tuff-breccia eruptives of undetermined origin.) 4. Foliated and layered breccia of low metamorphic grade that is rich in a variety of breccia clasts and that appears to correlate with units near the crest of the South Massif. (These rocks may be representatire of the youngest large-basin ejecta blankets in the region, possibly equivalent in mode of origin or even in age to the Fra Mauro Formation.) Although certainly complex internally, the dominant fabric of the North Massif apparently is that of roughly horizontal structural units that may be depositional or intrusive layers. In the South Massif, these units appear to be tilted westward or southwestward. High-angle normal faulting and tan-gray breccia intrusions apparently break the continuity of the structural fabrics in both massifs. The tilting and faulting of massif units may relate to their uplift during the Serenitatis impact event or subsequent major basin events (or both). A general similarity is evident in the visual and lithologic characteristics of the tan-gray and blue-gray breccias studied at the North and South Massifs. This similarity suggests that a general lithologic correlation can be made across the valley. The differences in rock characteristics may be explained by different ages of formation through similar processes or by different depths of burial (approximately 1.5 km in the North Massif and approximately 0.5 km in the South Massif). The Valley F Ioor and structural

very premature

conclusion on major portions of the stratigraphic sequence in the valley of Taurus-Littrow or on the nature of the processes by which this sequence came into being. The laboratory investigations have yet to be completed or to be integrated fully with the field observations. However, it is possible to summarize the probable stratigraphic sequences indicated by the field data and to list many of the interpretive alternatives for the petrogenesis of the major rocks and soils of the valley. The Massifs The oldest to youngest stratigraphic units that are present as bedrock in the North and South Massifs are as follows. (Interpretive statements are listed in parentheses.) 1. Light-gray breccia and crystalline rock as distinctive clasts in the blue-gray breccias. (These clasts may possibly be closety related to the differentiates of an early melted lunar crust.) 2. Crystalline, blue-gray, fragment.rich breccias and their metamorphic equivalents. (These breccias are possibly quenched and brecciated impact melts

The most

complex

stratigraphic

problems in the Taurus-Littrow valley are those of the valley floor and the materials beneath it. This complexity is introduced by two factors. First, there is the very great absolute age, approximately 3.7 billion years, of the orange/black glass deposit at Shorty Crater (ref. 5-5) and its relatively young exposure age, approximately 8 million years (ref. 5-6). Presumably, these ages apply to similar glasses in the dark floor materials. Second, there is the discovery of a thick (greater than 15 m) breccia unit of regolithic character at Van Serg Crater.

5-20

APOLLO 17 PRELIMINARY SCIENCE REPORT environment may account for their rarity around other, possibly older craters such as Shorty. The existence of orange and black glasses and of subfloor basalt fragments in these breccias (sec. 7) strongly suggests that they are the product of the general long-term regolith development in the valley. Taking into account these considerations and the field evidence described previously, the following general subsurface sequence, from the surface downward, seems probable for the valley. 1. An average of 15 to 20 cm of new, very weakly coherent regolith on the present dark valley floor surface 2. An average of 1 to 2 m of mixed basaltic debris and orange/black glass having generally mantling relationships to most large craters and boulders 3. A zone of variable thickness, possibly from 10 to 20 m, containing interlayered dark floor material and the ejecta blankets from Steno- and Camelot-age impact events (Much of this material may be similar to the Van Serg breccia.) 4. A zone gradational with the zone above (item 3) consisting of regolithic debris derived from the subfloor basalts and possibly interlayered with orange/black glass zones 5. A few meters thick basalt flow or ejecta blanket, either of which probably is presently discontinuous in distribution but which protects portions of underlying deposits of orange/black glass 6. A deposit of orange/black glass of unknown thickness, also presently discontinuous 7. A few meters of regolith developed on underlying basalt 8. At least 100 m of coarse-grained snbfloor basalt, the fine-grained portions of which have been largely incorporated into overlying regolith (The uniformity in the texture of ejected basaltic blocks throughout the valley strongly suggests that a single thick coofing unit of basalt may have filled the valley.) The Light Mantle All indications are that the light mantle was deposited as a single dynamic event on the dark floor materials that cover the valley. The materials of the light mantle appear to be identical to those of the South Massif talus, although vertical size sorting has probably occurred in the light mantle. Our observations tend to support the tentative conclusion of R.

The purity, the geometric constraints, and the petrographic characteristics (sec. 7) of the orange/ black glass deposit at Shorty Crater and the relative ages of the deposit require the following to hold true for its glasses, 1. The glasses were deposited at the lunar surface over a major unit of subfloor basalt or on an early regolith unit derived from the subfloor basalt, 2. The glasses were then almost immediately protected from regolithic mixing at the surface, possibly by an ejecta blanket or by a thin basaltic flow, for a period of approximately 3.7 billion years, 3. The glasses were then ejected onto or intruded into tile rim of Shorty Crater less than 8 million years ago, producing a very restrictive geometric situation, Glasses similar to the orange/black glasses have been reported mixed with basaltic debris in the dark floor materials (sec. 7). The apparently recent mantling over the valley craters by dark floor materials and the apparently thin regolith developed on these materials impose other general constraints on their stratigraphy and origin. The indications are very strong that since the formation of a widespread mantling deposit of orange/black glass approximately 3.7 billion years ago, some other process has acted more or less continuously to recycle this glass and produce the presently observed young mantling relationships, In view of the presence of certain low-temperature volatile components in the orange/black glasses (sec. 7), it is possible that impact events in the general size range of Shorty Crater will trigger the release of such gas as a fluidizing medium for local remobilization and extrusion. The known field characteristics of the orange/black glass deposits and of the dark floor material are reconcilable with a process of this nature acting in and around impact craters of 25 to 100 m in diameter. Also, a similar process has been observed to occur at the 500-ton Dial Pack event (ref. 5-7) in Canada as a result of the explosive pressurization of water-saturated sand in a layer well below the floor of the crater produced by the explosion. The other complicating factor in the interpretation of the valley floor is the great thickness of coherent regolithic breccias at Van Serg Crater relative to other portions of the valley. This thickness may be related to the position of Van Serg Crater on superposed ejecta blankets from Cochise and Shakespeare Craters. Also, the apparently rapid degradation of the Van Serg-type matrix-rich breccias in the valley

A GEOLOGICAL

INVESTIGATION

OF THE TAURUS-LITTROW

VALLEY

5-21

Shreve i and the Apollo soil mechanics team (sec. 8) that the light mantle originated through an avalanche, or fluidized flow, of South Massif talus with fluidization provided by solar wind gases adsorbed within the

original talus materials, The probable internal structure of the light mantle f_om the surface downward appears to be as follows, 1. 5 to I0 cm of medium-gray soil (regolith?) 2. Approximately 1 m of light-gray debris contaming few fragments larger than a few centimeters in diameter 3. Variable thicknesses of light-gray material containing numerous rock fragments larger than a few centimeters in diameter 4. A basal zone of mixing between light mantle and dark floor materials that may be marbled in texture This is the last major report of crew observations

obtained during the Apollo explorations of the Moon. We are confident that the future holds many other such reports as man continues his exploration of the frontier of the Earth and his use of the space environment. It is our belief that, as in past explorations, man's abilities and spirit will continue to be the foundation of his evolution into satisfaction from this evolution being there. The Apollo crewmen their singular opportunity of having ACKNOWLEDGMENTS; Few, it"any, exploration efforts in history better illustrate the inherent ability that exists within a large group of experienced and motivated men and women to plan, to implement, and then to react with clear good judgment to the unexpected. The success of this effort in the Apollo Program is to the everlasting credit of the thousands of the universe. Full only comes with deeply appreciate been there.

SU M MAR Y O F R ESU LTS The Apollo 17 lunar module (LM) hmded on the flat floor of a deep narrow valley that embays the mountainous highlands at the eastern rim of the Serenitatis basin. Serenitatis, the site of z pronounced mascon, is one of the major multi-ringed basins on the near side of the Moon. The Taurus-Littrow valley, which is radial to the Serenitatis basin, is interpreted as a deep graben formed by structural adjustment of lunar crustal material to the Serenitatis impact. During their stay on the lunar surface, the Apollo 17 crew traversed a total of _30 km, collected nearly 120 kg of rocks and soil, and took more than 2200 photographs. Their traverses, sampling, direct observations, and photographs span the full width of the Taurus-Littrow valley, The highlands surrounding the valley can be divided on the basis of morphology into (1) high smooth massifs; (2) smaller, closely spaced domical hills referred to as the Sculptured Hills; and (3) materials of low hills adjacent to the massifs and the Sculptured Hills. Boulders that had rolled down the slopes of the massifs north and south of the valley provided samples of that area. These boulders are composed of complex breccias that are generally similar to those returned from the Apollo 15 and 16 missions. Materials of the valley fill were sampled at many stations. Ejecta around many craters on the valley

floor consists of basalt, showing that the graben was partly filled by lava flows. A relatively thick layer (_15 m) of unconsolidated material overlies the subfloor basalt; this debris consists largely of finely comminuted material typical of the lunar regolith. The surface material over much Qf the TaurusLittrow region has a very tow albedo and was believed to be a thin young mantle, possibly pyroclastic, that covered the valley floor and parts of the adjacent highlands. No clear evidence of the existence of such a mantle as a discrete layered unit has yet been found, but it may be mixed in with the more typical debris of the lunar regolith. An unusual bright deposit extends across the valley floor from the foot of the South Massif. This deposit consists of breccias similar to those of the massif and is interpreted as an avalanche generated on the massif slopes. South Massif materials were collected from three breccia boulders that were probably derived from a blocky area near the top of the massif where a blue-gray unit overlying tan-gray material is exposed. Boulder 1, sampled at station 2, is a foliated and layered breccia, the only one of its type seen by the crew. The four samples collected from boulder 1 are breccias composed of dark-gray fine-grained lithic clasts in a light-gray friable matrix. Boulder 2, sampled at the South Massif, is a fractured rock from which five samples of vuggy, annealed, greenish-gray breccia were collected. A breccia clast and its host were sampled from boulder 3 at the South Massif. The clast is light-greenish-gray breccia with abundant mineral clasts and sparse lithic clasts. The matrix of the clast consists largely of angular fragments of a mafic silicate embedded in a very-fine-grained groundmass. The host material is a blue-gray breccia with scattered vesicles. 6-1

APOLLO 17 PRELIMINARY SCIENCE REPORT Smaller chips collected at stations 6 and 7 include the major rock types of the two large boulders, as well as a few other breccia types, one coarse-grained gabbroic rock, and one light-colored fine-grained hornfels. A few basalt fragments that are probable ejecta from the valley floor were also collected. The South Massif boulders most probably came from the highest part of the massif (boulder 1, station 2, from the blue-gray unit; boulder 2, station 2, from the underlying tan-gray unit), and the station 6 and 7 boulders probably came from within the lower third of the North Massif. Hence, two different stratigraphic intervals may have been sampled. Conversely, the lithologies of the South Massif boulders closely resemble those of the North Massif boulders in many respects. The similarity seen in early examination suggests the possibility that only one stratigraphic unit is represented. Whichever the case, the massifs are composed of intensely shocked breccias reasonably interpreted as ejecta from ancient large impact basins. On the accessible part of the Sculptured Hills, hand-sized samples are essentially absent, and no boulders that clearly represent Sculptured Hills bedrock were found. Small fragments of basalt, probably ejected from the valley floor, and regolith breccia dominate the samples, which consist mainly of chips collected with soils or by raking. Samples of friable feldspathic breccia from the wall of a 15-m crater and of a glass-covered gabbroic boulder that is almost certainly exotic were also collected. The greater dissection, lower slopes, lack of large boulders, and limited sample suite suggest that the Sculptured Hills may be underlain by less coherent breccias than the massifs. Subsequent to the formation of the TaurusLittrow graben by the Serenitatis impact, the valley floor was inundated and leveled by basaltic lava flows. Geophysical evidence (secs. 10 and 13)suggests that the prism of basalt filling the valley is more than a kilometer thick. The uppermost 130 m was sampled in the ejecta of craters on the valley floor. In general, the subfloor basalt blocks seen at the landing site were not visibly shocked or even intensely fractured. In some rocks, planar partings parallel bands expressed as differing concentrations of vesicles. Almost all returned samples of basalt can be divided into five classes: (1) vesicular, porphyritic, coarse-grained basalts; (2) vesicular coarse-grained basalts; (3) vesicular fine-grained basalts; (4) dense

Materials of the North Massif were sampled primarily from a 6- by 10- by 18-m fra_nented boulder at station 6 and a 3-m boulder at station 7. The station 6 boulder, which broke into five pieces, is at the lower end of a boulder track the apparent beginning of which is in an area of light boulders approximately one-third of the way up the massif. Photographs using the 500-ram lens demonstrate that dark boulders are abundant higher on the mountain, and light boulders occur again in the upper part. Thus, there may be a layer or lenses of darker rock high on the mountain with lighter rocks both above and below. The source of the station 7 boulder on the North Massif is unknown, but the boulder contains rock types like those of the station 6 boulders, Four of the five large pieces of the station 6 boulder were sampled. The boulder consists of two major breccia types, greenish-gray and blue-gray, They are in contact in a 0.5-m-wide zone that appears to be an area of mixing between the two rock types, The greenish-gray breccia is tough and annealed, with sparse lithic and mineral clasts set in a vuggy fine-grained matrix, Samples of blue-gray breccia from the station 6 boulder contain a high proportion (40 to 60 percent) of blue-gray breccia fragments in a vuggy greenishgray matrix. The matrix is a tough, finely crystalline material. Large friable inclusions ranging from 1 em to 1 m across are in sharp irregular contact with the blue-gray breccia. Samples of one of these are very-light-gray cataclasites, The station 6 boulder is intricately sheared, Comparison with the oriented returned samples shows that movement along some of the shear planes has deformed the clasts. Major events recorded in the station 6 boulder are the formation of the light cataclasite, its incorporation in the blue-gray breccia, and subsequent enclosure of the blue-gray breccia in the greenish-graybreccia, The station 7 boulder is similar to the station 6 boulder in that the two major rock types, greenishgray breccia and blue-gray breccia, are present. A large white clast (1.5 by 0.5 m), similar to those in the station 6 boulder, is penetrated by narrow blue-gray breccia dikes. The blue-gray breccia is in sharp irregular contact with the younger greenish-gray breccia. Like the station 6 boulder, the station 7 boulder is intricately fractured. At least two fracture sets are confined to the large white cataclasite inclusion and the blue-gray breccia,

PRELIMINARY GEOLOGIC INVESTIGATION OF THE LANDING SITE aphanitic basalts; and (5)vesicular aphanitic basalts. Before final accumulation of the Serenitatis mare fill, broad arching east of the Serenitatis basin tilted the subfloor lavas to the east, forming the present 1° eastward tilt of the valley floor. The subfloor basalt is overlain by fra_nental debris --_15 m thick. For the most part, this is impact-generated regolith similar to that developed on mare basalts elsewhere on the Moon. The central cluster ejecta, the light mantle, and the ejecta of Shorty and Van Serg Craters are discrete deposits recognized within the regolith. The lower part of the regolith is thought to be represented in the abundant dark friable breccias in the ejecta of the 90-m-diameter Van Serg Crater. The breccias contain scattered, light-colored lithic clasts as well as abundant dark glass, mineral and lithic fragments derived from basalts, and variable percentages of orange glass spheres and fragments. They are interpreted to be regolith breccias indurated and excavated from the deeper, older part of the regolith by the Van Serg impact. Basalt bedrock is not known to have been excavated by Van Serg. The central cluster ejecta is derived from the cluster of craters south and east of the LM. It is distinguished by the abundance of blocks in the unit, and the unit is too young for the blocks to have been reduced much in size by later impacts. All sampled blocks in the central cluster ejecta are subfloor basalt, The young pyroclastic dark mantle anticipated before the mission was not recognized in the traverse area as a discrete surface layer. Strong photogeologic evidence for the existence of such a mantle on the valley floor and in parts of the highlands still exists, Albedo measurements show that abnormal surface darkening, consistent with the concept of the introduction of exotic dark material-the "dark mantle"increases to the east and south in the Taurus-Littrow area. If the dark mantle is younger than the central cluster ejecta, it must be so thin in the landing site that it is thoroughly intermixed with the younger part of the regolith. Such mixed dark mantle may be represented by the dark glass spheres that abound in the soils of the valley floor. An alternative hypothesis is that the dark mantle may have accumulated shortly after the extrusion of the subfloor basalt. In this case, the deposit would be intimately mixed with subsequently formed regolith, The light mantle is an unusual deposit of highalbedo material with finger-like projections that extend 6 km across dark plains from the South

6-3

Massif. Rock fragments collected from the light mantle are similar in lithology to the breccias of the South Massif. This similarity supports the hypothesis that the light mantle is an avalanche deposit formed from loose materials on the face of the South Massif. A cluster of secondary craters on the top of the South Massif may record the impact event that initiated the avalanche. Size-frequency distribution and morphologies of craters on the light mantle suggest that its age is comparable to that of Tycho Crater, on the order of 100 million years. Shorty is a l l0-m-diameter impact crater penetrating the light mantle. Unusual orange soil was identifled in two places on the rim of Shorty Crater and in the ejecta from a small crater on the inner wall. A trench on the crater rim exposed an 80-cm-wide zone of orange soil, now known to consist largely of orange glass spheres. A double drive tube sample showed that the orange soil overlies black fine-grained material (now known to consist of tiny, opaque, black spheres) at a depth of _ 25 cm. The old age for the orange glass material implies solidification shortly after the period of subfloor basalt volcanism. The black and orange glass material, whatever its origin, must have been present in the Shorty target area; it was excavated or mobilized by the Shorty impact. Fine-grained soil, darker than the underlying unconsolidated debris, was recognized at the surface at Shorty Crater, at Van Serg Crater, on the light mantle, and on the massif talus. The soil is thin (e.g., 0.5 cm at Shorty, _ 7 cm on the flank of Van Serg) and probably represents the regolith that has formed on these young ejecta or talus surfaces. Relatively young structural deformation in the landing area is recorded by the Lee-Lincoln Scarp and by small fresh grabens that trend northwest across the light mantle. The sharp knickpoint at the base of the massifs may indicate that some fairly recent uplift of the massifs has kept the talus slopes active. INTRODUCTION Premission Geologic Studies

The Taurus-Littrow region lies on the southeastern rim of the Serenitatis basin (fig. 6-1) in an area of mountains, low hills, and plains. Serenitatis is one of the major multi-ringed basins on the near side of the Moon and is the site of a pronounced mascon. The landing site (lat. 20010 , N, long. 30°46 t E)islocated

6-4

APOLLO 17 PRELIMINARY SCIENCE REPORT

I
0

I
10

t
20 km

I
30

I

FIGURE 6-1.-Index map showing the Apollo 17 landing site and major geographic features of the Taurus-Littrow region (Apollo 17 metric camera frame AS17-0447).

on the gently inclined floor of a narrow flat-floored valley. The wails of the valley rise 2000 in above the floor. The valley is interpreted as a deep graben formed at the time of the Serenitatis impact, The highlands surrounding the valley can be divided on the basis of morphology into (1) high smooth massifs, (2) smaller, closely spaced domical hills referred to as the Sculptured Hills, and (3) low hills adjacent to the massifs and the Sculptured Hills (refs. 6-1 and 6-2). The highlands were interpreted in premission studies as deposits of ejecta derived from surrounding basins with major uplift occurring in the Serenitatis event. A possible volcanic origin was also considered but thought to be less likely (ref. 6-1). The reason for the morphologic difference between the massifs and the Sculptured Hills was not clear;

possibly, the difference reflects different responses to the Serenitatis event and to later tectonic forces. The low hills unit was considered to be downfaulted and partly buried blocks of massif or Sculptured Hills material. The nearly level valley floor was apparently formed by deep filling of the graben by fluid plains-forming material (subfloor unit). The material at the surface of much of the Taurus-Littrow region has a very low albedo and was believed to be a thin mantle, possibly pyroclastic, that covered the valley floor and parts of the adjacent highlands. Overlap relations with the typical mare material of Mare Serenitatis and an apparent deficiency of small craters indicated that the dark mantle might be very young in the lunar geologic time scale (refs. 6-1 and 6-3).

PRELIMINARY GEOLOGIC INVESTIGATION OF THE LANDING SITE Although quantitatively a minor deposit, its significance lay in its apparent young age and presumed volcanic origin. No volcanic rocks younger than 3.1 billion years had been returned before the Apolto 17 mission. Similar dark mantling deposits occur in relatively small tracts on the southwestern rim of the Serenitatis basin, at the outer edge of several other circular maria (ref. 6-4), and in other isolated patches on the lunar near side. A contrasting unit of bright mantling material occurs in a limited area of the valley. This unusual deposit extends from the southern wall of the valley northeastward in finger-like extensions across the dark valley floor. The material was interpreted as an avalanche from the steep slope of the South Massif (ref. 6-3). Geologic Objectivesand General Results

6-5

broad station coverage was designed to yield maximum information about the lateral continuity of massif lithologies. The principal sampling areas for valley materials were planned at stations 1, 4, 5, 9, and 10B. This coverage was designed to allow detailed stratigraphic studies of both the dark mantle and the subfloor unit. Craters that were to be visited on the valley floor potentially offered samples of subfloor material from depths as great as 150 m. Regolith was, of course, expected throughout the traversed regions, but an unusually small thickness was anticipated because of the low crater density on the dark and light mantle units. Boulders that had rolled down the slopes of the massifs north and south of the valley provided samples of that area. These boulders are composed of complex breccias; their general similarity to breccias returned from the Apollo 15 and 16 missions indicates that they are very ancient materials as anticipated. Their relation to the circular basins on the lunar near side is discussed subsequently. Crew observations and photographic evidence suggest that the materials of the massifs are layered and that at least two separate layers were sampled. Materials of the valley fill were sampled at numerous stations around the LM and en route to and from the massifs. Ejecta around many craters on the valley floor consists of basalt, confirming that volcanic materials underlie the Taurus-Littrow valley floor. A relatively deep layer of unconsolidated material overlies the subfloor basalt; this debris consists of finely comminuted material typical of the lunar regolith. It may also contain the dark mantle mapped in premission studies. No clear evidence for the existence of a dark mantle as a discrete layered unit has yet been found, but it may well be mixed in with the more typical debris of the lunar regolith. The bright deposit extending across the wdley floor from the foot of the South Massif consists ofbreccias similar to those of the massif; the interpreted origin of this deposit as a landslide thus appears to be confirmed. Traverse Data

The geologic objectives of the Apollo 17 mission may be divided into orbital and lunar surface data collection. The orbital objectives in the TaurusLittrow area were to add to the knowledge of the regional geology of the site through direct visual observation and photographs and to assist in locating the LM on the surface. Additional aid in traverse location by panoramic camera photographs of the lunar roving vehicle (LRV) tracks and crew-disturbed areas was anticipated. The principal objectives of the ground crew were to deploy file Apollo lunar surface - experiments package (ALSEP) and the surface electri\cal properties (SEP) experiment; to record gravity data on the traverse gravimeter; to describe the kinds and proportions of rocks in the various map units and to collect samples of them; to observe, describe, and collect samples of regolith and dark mantle that were thought to cover most of these units; to look for outcrop and, if found, to describe, photograph, and sample it; to describe structures, including lineaments, layers, and faults, in various units; and to observe and describe, where possible, the attitudes of and contacts between the major geologic units, In detail, ground objectives were planned around groups of stations with the potential of yielding varied geologic information (fig. 6-2). The prime sampling areas of the massif and Sculptured Hills units were located in the station 2, 6 and 7, and 8 areas, as well as between stations 2 and 4, on the assumption that the light mantle unit was composed of materials derived from the South Massif. This

The Apollo 17 crew traversed _ 2 km during the first period of extravehicular activity (EVA), 18 km during EVA-2, and 10 km during EVA-3 for a total of _30 km. Nearly 120 kg of rocks and soil were collected and more than 2200 photographs were taken on the lunar surface. An index map of the

FIGURE 6-2. Preplanned traverses and geologic objectives. traverse area is shown in figure 6-3. Figure 6-4 shows the traverse path and stations in detail, and table 6-I lists map coordinates for traverse points. The lunar surface orientations of some of the Apollo 17 rock samples at the time of their collection are shown in appendix A (p. 6-60). Panoramic views and detailed planimetric maps of the traverse stations are shown in appendix B (p. 6-73). STRATIGRAPHY AND PETROGRAPHY

The studied and sampled geologic units are described in approximate stratigraphic order. However, some parts of the sequence, such as the relative ages of the massifs and the Sculptured Hills units, are not well known. Similarly, regolith units and surficial deposits on the highlands and on the valley floor

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6-7

iii iiiiiiii I 0 I 1 I 2 I 3

km FIGURE 6-3.-Index of the traverse area. Lettered boxes (A through F) show boundaries of detailed traverse maps (figs. 6-4(a) to 64(f)) (Apollo 17 panoramic camera frame AS17-2309). overlap in time. In neither case is rigorous chronology of development implied by the order of discussion, Table 6-II summarizes the stratigraphy as seen in the field by the crew. Changes from lunar surface terminology are indicated at the appropriate place in the text. Table 6.II1 relates the field terminology to sampling areas, representative samples, and laboratory terminology, composed of light-tan materials stratigraphically overlain by blue-gray materials (appendix B, fig. 6-109). A concentration of boulders occurs at and near the break in slope at tile foot of the South Massif (fig. 6-5). Those boulders with visible tracks on the massif slopes (fig. 6-6) were emplaced after the avalanche that formed the light mantle, and probably emplacement of all the boulders postdates the light mantle. If they were a part of the avalanche itself, the boulders would be more uniformly distributed across the surface of the light mantle rather than concentrated near the base of the massif. Most of the boulders probably rolled from blocky areas that may be outcrops high on the massif

South

Massif

South Massif materials were collected from just above the break in slope at the base of the South Massif at station 2. The crew described the massif as

aCoordinate system is that used in the premission data package. bLRV-1, LRV-2 (etc.) refer to stations where samples were collected from the LRV with a long-handled sampling tool. Station 2A (LRV-4) was an unplanned station at which the crew dismounted from the LRV. EP-7 was the seventh ._ km 1_.0 explosive package used in the LSPE and the only explosive package that was not located at a sampling station.

fig. 6-7).

These

bouldery

areas

are

mostly

in the type have been identified with certainty in the photographs. The boulder is _ 2 m across by 1 m high above the ground surface. It has a well-developed fillet _ 30 cm high on its uphill side and no fillet on its downhill side. The boulder appears to be highly eroded and has a hac!dy and knobby surface. The knobs range from < 1 to 15 cm across and were reported by the crew to be mostly fine-grained clasts eroded from a more friable fine-grained matrix. The crew also reported dark elongate clasts parallel to the bedding planes (S a in fig. 6-8); these are not discernible in the photographs. Based on the degree to which the bedding foliation is developed and on the erosion-produced characteristics, which are presumably related to the friability of

blue-gray unit. No apparent source for the boulders is visible on the lower two-thirds of the massif. The three boulders sampled at station 2 have no visible tracks on the massif slope. However, the boulders in the station 2 area are directly below a blocky area just above the contact between the blue-gray unit (above) and the tan-gray unit (below) (figs. 6-5 and 6-6). The three boulders are _ 50 m above the break in slope at the base of the South Massif in the field of boulders strewn near the base (fig. 6-5). Station 2, Boulder 1

Boulder l, the first boulder sampled at station 2, is a layered and foliated rock (fig. 6_g), the only one of this type seen by the crew. No other rocks of this

APOLLO 17 PRELIMINARY SCIENCE REPORT were taken from boulder I (fig. 6-8). All samples are breccias with light-gray friable matrices (called tan breccia by the crew) containing dark-gray fine-grained lithic clasts. Sample 72215 is possibly a clast eroded from the friable matrix of the zone in which it occurred within the boulder. All the samples contain distinctive light-gray clasts with thin dark-gray selvages. Station 2, Boulder 2

the matrix, the boulder is divided into five crudely layered zones (fig. 6-8). A fairly well-developed set of cleavage planes (Sb in fig. 6-8) that are roughly at fight angles to the bedding planes is visible across the middle of the boulder, and a similar set with the same orientation occurs in sample 72255. These are probably shear planes. The eroded nature of the boulder and the well-developed fillet on its uphill side suggest that it has been in its present position for a considerable period of time. Four samples (72215, 72235, 72255, and 72275)

I

The second boulder, a greenish-gray breccia sampled at station 2, is _ 2 m across and 2 m high above the ground surface. It is rounded but smoother than boulder i, which suggests that boulder 2 is more uniform than boulder 1. A poorly developed set of fractures (Sa) trends from upper left to lower right as seen in figure 6-9. Tiffs set dips gently at _ 5 ° into fire surface of the rock and probably controls the

N
N
FIGURE 6-5.-Part of the South Massifshowingarea sampled at station 2. Boulders are numbered in order of sampling and text discussion.Bright-rimmedcrater (20-m diameter) above and to left of samplearea is identified in figure 6-6. Probable source of boulder track shown in figure 6-6 is boulder field centered on the skyline in this view (AS17-138-2t 072).

FIGURE 6-6,-Boulder tracks on the South Massif in the vicinity of station 2.

FIGURE 6-7.-Telephotographic mosaic of boulder concentrations near the top of the South Massif. Probable source area of station 2 boulders is shown in left frame (AS17-144-22051 to 22057).

seen m the photographs. The boulder has a moderately well-developed fillet _ 0.25 m high on its uphill side but overhangs the ground surface on its downhill side. Five samples (72315, 72335, 72355, 72375, and 72395) were taken from the second boulder at station 2 (fig. 6-10). Two of these samples (72315 and 72335) were taken from a 0.5-m clast at the lower edge of a spalled area, and the remaining three •

Two relatively friable zones are visible in the photographs (fig. 6-9) and may also be clasts. These were not sampled. All five samples are vuggy greenish-gray breccias and, except for having smaller cavities, appear to be very similar to rocks called anorthositic gabbro by the crew at station 6. Lithic clasts, rarely more than 10 mm in diameter, are principally fine-grained homfelses, but a few are cataclastically deformed plagioclase-rich rocks. Mineral clasts in-

clude angular fragments of plagioclase silicate mineral as large as 4 mm.

and a mafic

Station 2, Boulder 3
Boulder 3 isan equant, subangular breccia boulder 40 cm across. Its surface is rough on a scale of--_ 1 to 2 cm. Several 2- to 4-cm clasts and one lO-cm light-gray clast in a gray matrix are visible in the photograph (fig. 6-1 I). No well-developed fracture or cleavage sets are visible, but two well-developed planar fractures at -_ 90 ° to one another are visible. A third fracture, approximately parallel to the upper rock surface, is also visible, The boulder has a poorly developed fillet, which, together with its subangular shape, suggests that it has

been in its present position for a relatively short period of time. Two samples, 72415 and 72418 (a clast) and 72435 (matrix), were taken from the third boulder at station 2 (fig. 6-12). Sample 72435 is a blue-gray breccia that contains _ l0 percent lithic and mineral clasts in a tough, finely crystalline, deep-bluish-gray matrix. The rock has a local concentration of slit-like cavities in its matrix that are elongate parallel to a weak alinement of lithic clasts. The clast from this boulder represented by samples 72415 to 72418) is a light-greenish-gray breccia (with color but no stratigraphic implications) composed of abundant mafic silicate mineral clasts and sparse feldspathic lithic clasts set in a matrix, composed of the same constituents, that is moderately fine grained, and probably annealed. coherent,

6-16

APOLLO 17 PRELIMINARY SCIENCE REPORT by many large blocks and smaller fragments, most of which were derived from higher on the massif. There appears to be a bimodal distribution of fragments in the irea. Fragments smaller than 2 to 3 cm and larger than 15 to 20 cm are abundant, whereas fragments between these two sizes are relatively sparse. Fragments smaller than 50 cm are scattered randomly over the surface; larger ones are generally located in clusters that may be fragments from a single larger rock that had rolled or been thrown into that area. Where the soil was disturbed by the crew, it is medium gray on the surface and lighter gray beneath (fig. 6-13).

FIGURE 6-11.-Sketch map of boulder 3 at station 2 (AS17-137-20963).

Station

6Boulder

Most of the samples collected at station 6 are from a large (6 by 10 by 18 m), fragmented boulder (fig. 6-14) lying at the end of a boulder track (fig. 6-15) that extends approximately one-third of the way (_ 500 m) up the face of the massif. Two other boulder tracks appear to originate at approximately the same level (fig. 6-16). From this level to the top of the massif, boulder concentrations are common.

Stations 6 and 7 were designated as sampling sites for material that had been mass wasted from the North Massif. Station 6 lies on an 11 ° slope _ 20 m above the break in slope between the massif and the valley floor. Station 7 is _ 500 m east of station 6, on a 7° slope just above the break in slope (figs. 6-3 and 6-4). The surface in the area of the stations is covered FIGURE 6-13.-Area 6.of disturbed soil between boulders 3 and 4 at station Soil is lighter beneath the thin gray surface layer. The letter designations indicate planar surfaces onto which boulder 4 may fit. Face A is the most likely fit. See text for discussion (AS17-140-21434).

a layer or lenses of darker rock may exist high on the mountain. Lighter boulders occur above and below. The lower light zone was sampled at the station 6 boulder. are The station 6 boulder largest into 8 m across. that alined downslope. The broke is _ five pieces The original boulder can be pieced back together, generally with only a small amount of rotation mayany of the blocks. Several large fra_nents that of' have broken from the boulder as it rolled downhill can be seen in and around the boulder track (fig. 6-18). rotation until similar appearing faces fit together (fig. Boulders 4 and 5is can be vesicle foliation is in a 6-19). When this done, reassembled by minor similar orientation in each boulder, and nonvesicular inclusions in both pieces also fit across the break. Boulders 1 and 2 also fit without substantial manipulation. It appears that boulder 1 can be raised and placed against boulder 2 (fig. 6-20). Boulders 2 and 3 6-21). The relationship of the structural split between boulders 1, 2, and 3 and boulders 4 and 5 is not as are fitted together in much the same manner (fig. obvious, and the fit is still tentative. Figure 6-21 shows a nearly planar surface (A) on boulder 2, which dips approximately the same as the north face of boulder 4, as shown in figure 6-19. When boulder 4 is placed on this surface, the foliation, which appears to be planar concentrations of vesicles in boulder 2, is parallel with the foliation in boulders 4 and 5. Also, a series of widely spaced joints in boulder 4 is then alined with similar joints in boulder 2. A second, less-likely possibility is to place the north face of boulder 4 on planar surface (B) on borfider 2, adjacent to the one just described (fig. 6-13). However, structures seen in both boulders do not aline as well, and the shape of the fractured face of boulder 2 does not conform well with that of boulder 4. Four of the five numbered boulder fragments were sampled. Two major breccia types can be distinguished: greenish-gray and blue-gray breccias. The third, fourth, and fifth boulders and part of the second are greenish-gray breccias, described by the crew as anorthositic gabbros. In boulder 2, there is an irregular contact between the greenish-gray breccia and a blue-gray breccia. This zone, --_50 cm across, appears to be an area of mixing between the two rock types. Boulder 1 is also blue-gray breccia. Two samples were collected from the greenish-gray breccia. Sample 76215 is part of a larger rock that spalled from boulder 4, and 76015 is from the top of

5 I I 5 l0 m FIGURE 6-14.-Diagram of station 6 boulder shewing relationships of large fragments and possible points of reassembly. Sample locations are designated on boulder fragments, I 0

These boulder concentrations are probably derived from near-surface bedrock. At lower elevations, the bedrock in the massif is covered by a thick regolith arid talus cover. At higher elevations, the massif is covered by a much thinner layer of fine material that allows the underlying bedrock to be eas[ly excavated by the more abundant smaller cratering events. This is suggested by the change in slope from 25 ° in the upper two-thirds (upper 1000 m) of the massif to 21.5 ° in the lower one-third of the massif (_ 500 m above the base). One boulder track visible in figure 6-16 extends nearly 1000 m up the slope. At the lower end of this track is a large boulder that is darker than most of the other boulders on the lower one-third of the massif (fig. 6-17) and that is also darker than the station 6 boulders. A concentration of dark boulders occurs near its apparent source, and similar concentrations are scattered at approximately the same level elsewhere on the mountain face. Thus,

6-18

APOLLO

17 PRELIMINARY U V

SCIENCE

REPORT

4500 m

,of mosaic f o figu 6-4 re

4000 m

. Boundary f mosaic f o o figure6-6

FIGURE 6-15.-Footprints of 500-mm mosaics of part of the North Massif that are shown in figures 6-16 and 6-18. Features identified by letters are visible in figures 6-16 and 6-18; primed letters denote objects visible in figure 6-18 only. The 500-m grid begins at the LM site (Apollo 17 panoramic camera frame AS17-2309).

boulder 5 (fig. 6-19). These rocks are tough annealed breccias with sparse lithic and mineral clasts set in a vuggy fine-grained matrix. The vugs, which range in size from 0.1 mm to _ 9 cm, are flattened and locally alined. Around the larger cavities, the sugary intergrowth of minerals that forms the matrices of these rocks gradually coarsens over a distance of _ 1 cm. At cavity walls, individual minerals of the matrix become distinguishable, and the rock has a poikiloblastic texture. Lithic clasts, all < 1 cm across,

include granoblastic intergrowths of plagioclase and a yellow-green mineral. Two unsampled rock types are present within the greenish-gray breccia. Several baseball-sized light-gray clasts are scattered randomly throughout the rock. The clasts appear nonvesicular and are in sharp irregular contact with the greenish-gray breccia. On boulder 5 (fig. 6-22), a large (0.5 by 1 m), gray nonvuggy area is evident within the greenish-gray breccia. Photographs suggest that the nonvuggy rock

PRELIMINARY

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6-19

5000 m 45OO m
/ m

5000 m -1000m

4000 m

4500 m

-500 m I Bouldertrack 3500m

4000 m 500m

3000 rT Om

FIGURE 6-16. Mosaic of 500-mm photographs taken from LM area showing boulder tracks on the North Massif. Dashed lines indicate boulder concentrations. The grid perspective is the same as that in figure 6-15. Elevations of grid corners (in parentheses) were taken from the NASA Lunar Topographic Photomap, Taurus-Littrow, 1:25 000, first ed., Sept. 1972, by the Defense Mapping Agency. According to this map, the elevation of the landing point is 4510 m, and the summit of the North Massif is 6178 m. (AS17-144-21991, 22119 to 22122, and 22127 to 22130).

may differ only in texture, not composition, from the host breccia. The dense area is sharply bounded by vuggy breccia on two sides and grades into it on a third side. This area may be an inclusion that was incorporated in the greenish-gray breccia, which vesiculated along the margins, or a locally nonvesiculated interior of the boulder. The former is preferred because of the sharpness of the contact on two sides. A set of planar structures occurs within the dense material parallel to the fracture face between boulders 4 and 5. It is not clear what these structures are, but they do not appear to be compositional layers. They do not continue into the vuggy part of the boulder, which further suggests that the nonvesicular rock is an inclusion rather than a central nonvesiculated core of the boulder, Two samples from the blue-gray part of boulder 1 FIGURE 6-17. View of the North Massif showing principal elevation data on prominent boulder tracks. Samples were collected adjacent to Turning Point Rock (station LRV-10). The light color of Turning Point Rock and station 6 boulders in contrast to the dark color of the large rock that rolled from high on the North Massif is clearly evident (AS17-141-21550).

6-20

APOLLO

17 PRELIMINARY

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_500 4250 m_.

-250

0m 4250 m

_ j" -500m 3750 m, /

250m 4000rn

3750m / t -250m_" 3500 Station 6 boulderrac_t B_ 500 m

250m 500m FIGURE 6-18.-Telephotographic view of prominent boulder tracks on the lower North Massif showing probable source area of station 6 boulder. Lowercased letters indicate fragments that may have broken from station 6 boulder. The large boulder in the lower left, at the end of the prominent track that heads at an elevation of 5550 m, is distinctly darker than any others in this area; its darkness is characteristic of some boulder concentrations high on the mountain as seen in figure 6-16 (AS17-139-21252, 21254, 21262, and 21263).

76215

FIGURE 6-19.-Boulders 4 and 5 at station 6. Arrows indicate probable matchpoints between the two boulders (AS17-140-21414, 21416, 21418, 21429, 21432, and 21433).

PRELIMINARY GEOLOGIC INVESTIGATION OF THE LANDING SITE

6-21

FIGURE 6-20.-Boulders 1 and 2 at station 6. Arrows indicate probable matchpoints between boulders (AS17-140-21497). (fig. 6-23)(samples largely of blue-gray gray matrices. The samples is high (40 somewhat browner 76275 and 76295)are composed breccia clasts in vuggy greenishproportion of clasts in these two to 60 percent), and the matrix is and darker than the typical vuggy line blue-gray breccias that contain sparse finely recrystallized light-gray clasts. In the blue-gray breccia of boulder 1, there are light-gray friable inclusions ranging in size from 1 to 2 cm to 1 m across that are in sharp irregular contact with the blue-gray breccia. Eight small samples (76235 to 76239 and 76305 to 76307) are chips that represent one of these inclusions (fig. 6-24). These samples are very light-gray cataclasites composed of angular mineral debris that includes yellow-green and pale-grass-green mafic silicates and plagioclase. Two other types of inclusions in the blue-gray breccia were not sampled. There are a few inclusions

greenish-gray rocks. Vugs, which are _ 2 to 5 mm across, are in most cases lined by rich-b:rown pyroxene and plagioclase with or without ilmenite plates, The matrices of these samples are tough, finely crystalline material composed principally of angular mineral debris (plagioclase, yellow-green mineral, brown pyroxene) and small lithic fragments of bluegray breccia. The clasts are dominantly fine crystal-

6-22

APOLLO 17 PRELIMINARY SCIENCE REPORT is prominently foliated, with alternating layers of abundant or sparse blue-gray breccia clasts. The blue-gray breccia clasts contain sparse, sugary, white hornfels clasts and moderately abundant marie silicate fragments. The largest blue-gray clast in the rock has a string of vuggy patches 3 to 12 mm across of plagioclase and rich-brown pyroxene along one edge. Sample 76315, collected from boulder 2 near the contact, appears to be transitional between blue-gray breccia and the type represented by sample 76255. The rock is mainly blue-gray breccia with a few white clasts; a large (3 by 8 cm) white clast at one end of the specimen is veined by blue-gray material. Both components were subsequently weakly brecciated so that pieces of blue-gray rock are now encased in a white matrix. In boulder 1, several throughgoing planes (Sa through Sg) can be recognized in stereoscopic study of the photographs (figs. 6-23 and 6-25). The lettering sequence does not imply a sequence of development in the rocks. When comparing these planes with the oriented returned samples, it can be seen that they represent shear planes along some of which movement has occurred. Two types are evident. Along the Sa plane, shearing has deformed the clasts to create discontinuous compositional banding. The zoning in sample 76255 is parallel to the Sa shears. This type shear is closely spaced (a few centimenters or less), but it is not a plane that had any substantial control over the shape of the boulder because the fracture surfaces are discontinuous and

FIGURE 6-21.-Boulders 2 and 3 at station 6. Arrows indicate fractures that are alined when boulders are fitted together. Letter designations,particularly A, indicate planar surfaces onto which boulder 4 may fit. See text for discussion (AS17-146-22293).

: • '_'_ ,

the rock is coherent across these surfaces. Planes Sb and Sf are also this type. Planes Sc and Sd are typical of the second type; they appear to be somewhat more widely spaced planes that form fracture faces on the surface of the boulder. Sample 76295 parted along Sd when sampled. Planes S e and Sg are also this type. Most of the shears appear to penetrate the boulder. Planes Sa and Sb, for example, can be seen in two places on the boulder over a meter apart. Throughout the boulder, movement along the shears does not appear to have been uniform. In the area where sample 76255 was collected, one of the large light-gray clasts has been intensively sheared. The large elast from which samples 76235 to 76239 and 76305 to 76307 were collected has not been substantially deformed. The direction of shearing is the same in two areas, but the amount of movement is different. Two fracture sets (A and B in fig. 6-23), which have not been identified in the samples, are

(fig. 6-23, lower left) that are not as friable in appearance and are a darker gray than the light-gray inclusions sampled. A second type, which is rare, is medium gray and vesicular with sharp irregular boundaries (fig. 6-23, upper left), One sample (76255, collected from boulder 1) is a breccia that contains clasts of blue-gray set in a friable light-gray to brownish-gray matrix. The sample

major mutually perpendicular fractures that shape the south and east faces of the boulder, At least one and possibly two of these sets of shears can be seen in boulder 2. Sample 76315, collected near the contact in boulder 2, shows some evidence of shearing. In figure 6-26, the face shown on boulder 2 is parallel with the Sc structures of boulder 1. Figure 6-27 shows this face, together with what is probably an expression of the Sd planes. The other structures are probably in this boulder also; but, because of the lower resolution and the direction from which this photograph was taken, they are not visible. It does not appear that the Sc planes penetrate boulder 2 completely. They appear to die

out as the contact between the two breccia types is approached. Assuming that the boulders have been reassembled correctly, it is not evident that these shears are present in the greenish-gray breccia. Some planar structures can be seen on boulders 4 and 5, but they neither coincide with nor look the same as the shear planes seen in boulders t and 2. They are generally spaced several centimeters apart and appear to be fractures rather than the shear planes. No evidence of shearing is seen in samples 76015 and 76215 collected from these boulders. One of the first events represented in the station 6 boulder was the formation of the light-gray to white cataclasite. This breccia was enclosed by the blue-gray

breccia, either during the same event or a later one. The two unsampled clast types in the blue-gray breccia probably have similar histories. The blue-gray breccia was heated enough to allow minor vesiculation. The blue-gray breccia was then incorporated by the greenish-gray breccia, which must have been heated enough to allow intensive vesiculation. The

vesicles define a foliation parallel to the contact with the blue-gray breccia. The shearing seen in the blue-gray breccia portion of the boulder, which caused the banding seen in sample 76255, apparently occurred before and/or during its incorporation into the greenish-gray breccia, because no extension of these shears is evident in the greenish-gray breccia.

PRELIMINARY

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6-25

FIGURE 6-25. View of boulder 1 at station 6 after removal of samples; shows shear sets, Sa through Sg. Dashed area denotes a crushed zone with mixing between light-gray and blue-gray breccia. Note the large fracture face of blue-gray breccia with light-gray clasts (AS 17-140-21456).

The blue-gray breccia may, however, be more susceptible to shearing than the greenish-gray breccia, It is not clear whether the vesicular palch seen ir boulder 1 is of the same generation as the greenishgray breccia because its relation to the contact cannot be seen in three dimensions. The color and vesicularity of it suggest that it is the same; however, it is

not known if the vesicular patch was injected blue-gray zone during this time.

FIGURE 6-31.-Fractures in blue-gray breccia and light-gray inclusion in station 7 boulder. Note differences in spacing of fractures. (a) Photograph AS17-146-22310. (b) Sketch map. sample, and 76280 is a 6-cm-deep scoop of soil Another soil sample, 76320 (fig. 6-20), was collected from the north face of boulder 1. This soil was probably picked up by the boulder as it fell into its present position. Sample 76220 is soil collected from the center of the boulder track _ 10 m northwest of

FIGURE 6-32.-Station 7 boulder showing closely spaced fractures in a light-gray clast. (a) Photograph AS17-14622306. (b) Sketch map. Unlabeled lines show fracture traces. boulder 1. Approximately 5 m south of the LRV, a single drive tube, 76001, was collected. All these samples probably represent a mixture of breccia fragments from the massif and subfloor material, the major contribution derived from the massif. Rock samples from stations 6 and 7, other with than

PRELIMINARY GEOLOGIC INVESTIGATION OF THE LANDING SITE

6-29

Blue-gray matrix completely envelops pieces of the broken clast around its periphery, but the interior of the clast is incompletely penetrated by blue-gray matrix so that the fragments form a porous aggregate. The blue-gray matrix appears to be holocrystalline and fine grained and has a small proportion of smooth-walled vesicles and irregular vugs. Other clasts in the blue-gray matrix include a distinctive fragment that consists of 2-mm euhedral plagioclase crystals, interstitial light-brown pyroxene, annealed plagioclase-rich fragments, and mineral debris. Several basalts were collected in the rake and grab samples at these two stations: four vesicular, porphyritic, coarse-grained basalts (76037, 76538, 77535, and 77536); two vesicular fine-grained basalts (76136 and 77516); and two dense aphanitic basalts (76537 and 76539). The presence of the basalts indicates there is some mixing of subfloor materials in tile talus of the massif material. This area is also dovar range from the central crater cluster that dominates the ]FIGURE 6-33.-North face of boulder 4 showing permanently shadowed soil and references to other soil samples (AS17-140-21406). those collected from boulders and other than basalts, include five white cataclasites (76355, 76536, 76558, 76559, and 77017); 14 greenish-gray breccias (76055, 76556, 76557, 76577, 77035, 77515, 77517, 77518, 77519, 77525, 77526, 77637, 77539, and 77545); five blue-gray breccias (76036, 76035, 76555, 76569, and 76575); two light-gray breccias (76505 and 77538) with small blue-gray clasts in a moderately coherent matrix; six dark-matrix breccias with small white clasts (76506, 76545, 76546, 76547, 76548, 76549, 76565, 76566, and 76568); one coarsegrained gabbroic rock with _ 35 percent pyroxene (76535); one light-gray regolith breccia (76567); and one light-colored f'me-grained hornfels (76576). The cataclasites are chalky white rocks, but 77(117 is laced by dark glass veins and one side is covered by a thick coating of dark glass with many inclusions of cataclasite. The greenish-gray breccias inchide two large rocks (76055 and 77035) with irregularly distributed small flit-like cavities that are locally alined. A smaller sample grouped with the greenishgray breccias (77517) and two small pieces (77525 and 77526) that may have been broken from it have abundant medium light-gray to light-blue.gray aphanitic clasts in a vug-free, annealed, light-gray matrix, Sample 76035 is an unusual blue-gray breccia that contains a shattered clast of light-gray hornfels. landing area and that probably threw debris onto the slopes of the North Massif and adjacent Sculptured Hills. Sou Iptured H ills The single location on the Sculptured Hills from which samples were collected (station 8) lies _ 20 m above the valley floor on a southwest-facing slope just southeast of Wessex Cleft and 4 km northeast of the landing point. The station is within thezonemapped as dark mantle (refs. 6-1 and 6-5). This unit locally mantles the lower slopes and linear valleys of the Sculptured Hills (fig. 6-34) and is likely to have been mixed with the underlying regolith. The terrain is undulating on a general slope of 10° to 30 °, being steepest above the station 8 area (figs. 6-35 and 6-36). From a distance on earlier traverses, the crew described these hills as being pockmarked (by small craters), darker gray, more hummocky and lineated, and as having lower slopes than the massifs. During late mission orbits under highest Sun elevations (58°), the hills were characterized as incorporating "the albedo both of the North Massif and the (dark) mantle area.., to give.., an in-between gray albedo, but the sculpturing is produced by the darker albedo that looks like the mantle and the lighter albedo that looks like the massif." These observations are borne out by both the high Sun orbital and the surface photographs. While approaching the hills, the crew noted that

6-30

APOLLO 17 PRELIMINARY SCIENCE REPORT

I

km

North Massif

FIGURE 6-35.-Station 8 area at Sculptured Hills as viewed from the LM, 4 km away. Note the contrast between the hills on the right and the massif material directly above WessexCleft, although both slopes have similar orientations (AS17-137-20876). FIGURE 6-34.-Panoramic camera view of station 8 area showing distribution of dark mantle on the Sculptured Hills, WessexCleft, and valleyfloor (Apollo 15 panoramic camera frame AS15-9557). rocks larger than 20 cm are very rare on the Sculptured Hills slopes compared with their relative abundance at the foot of the North and South Massifs. Most of the fragments are small clods and create a downslope pattern of small lineaments indicating youthful mass wasting on currently active slopes (appendix B, fig. 6-121). However, the three boulders investigated on this slope showed no evidence of having moved downslope, and the only other large rocks on the hill are described as farther upslope. These latter blocks are the fragments visible within the patches of dark mantle in figure 6-36. The few fragments seen on the local surface are subrounded to subangular; some are partly buried, but the two sampled boulders and most of the soil clods are perched on the surface. The lack of blocks around fresh craters as large as 50 m in diameter (fig. 6-36) indicates that bedrock is more than 10 m below the surface slope material. The soil in this area, at least to the 20- to 25-cm depth of the trench samples, consists of fine-grained cohesive clods and particles, The soil has a moderately dark appearance characteristic of the mantle throughout the valley floor, No large craters are present in the immediate area; those as large as several meters in diameter are common, however, and have a continuum of morphologies from fresh-appearing, topographically sharp features to highly subdued depressions. The craters have neither prominently raised nor blocky rims, although one secondary crater lower on the slope (fig. 6-37) forms a cloddy rim similar to that sampled from the LRV on the rim of SWP Crater (LRV-11, fig. 6-34). The sample suite collected at the foot of the Sculptured Hills is represented mainly by basalts that are most likely ejecta deposited on the Sculptured Hills slopes by valley floor craters and subsequently concentrated by mass wasting toward the base of the hills. The samples are all from the subtle dark-gray apron interpreted on premission maps as dark mantle (fig. 6-34). One large basalt fragment (sample 78135, fig. 6-38) was taken from near a half-meter-wide boulder, probably also basalt, that was too hard to be sampled directly. Other basalt fragments were collected in the rake and soil samples. The basalts are not obviously shocked or glass veined, and the crew indicated the basalts resembled others sampled at different localities on the valley floor. Perhaps the more important samples for interpreting the lithologic nature of the Sculptured Hills are represented by the smaller rocks and soils. Unfortunately, their relationship to the underlying hills is not known. The friable feldspathic breccia (sample 78155) collected from the wall of a 15-m crater is a particularly good candidate for Sculptured Hills material. Its friability and color are compatible with the more rounded topography of the Sculptured

FIGURE 6-36.-Telephotographic mosaic of Sculptured Hills slope above station 8 as viewed from station 2A. Sun elevation is 28 ° (AS17-144-22034 and 22035).

6-32

APOLLO 17 PRELIMINARY SCIENCE REPORT

FIGURE 6-37.-Cloddy secondary crater on slope below station 8. Break in slope is _200 m from camera(AS17-142-21741). Hills, the general absence of boulders, and the light-colored, generally fine-grained ejecta seen in the largest craters of this area. Samples larger than 1 cm taken from soil bags and the rake samples include 22 dark-matrix breccias, most of which have small, white, lithic fragments and clasts of mare basalt (78508, 78516, 78518, 78535 to 78539, 78545 to 78549, 78555 to 78559, and 78565 to 78568), one rock composed of regolith clods loosely cemented by glass (78525), one dunite(?) (78526), one nonvesicular metaclastic rock (78527), and one white feldspathic breccia (78517). The gabbroic rocks (samples 78235 to 78238, 78255, and 78256) are from the top and bottom of another half-meter-size boulder. The rock is coarse grained, composed of _ 50 percent each of plagioclase and pyroxene, intensely shocked, and heavily glass coated and glass veined (figs. 6-39 and 6-40). No fillet existed on the boulder in its original position. These properties and its strongly fluted, glassy surface suggest that it originated from outside the sample area and was emplaced relatively recently at station 8. The lack of blocky craters or related boulder tracks upslope argues against a local source. The well-documented trench samples (78420 to 78480) have not been described yet, but they should typify the soils of the lower slopes of the Sculptured Hills. They are probably a mixture of valley floor debris and Sculptured Hills soils. The soil sample collected from a dark cloddy crater on the rim of SWP Crater (78120) at LRV-11 was just at the base of the slope and may represent either deeper material from SWP Crater or mass-wasted material from upslope (fig. 6-34). Perhaps the original composition of the hills can best be determined by subtracting from these soils the average composition of the typical valley floor.

Between the Massifs and the Sculptured Hills The upper slopes of the North, South, and East Massifs are alike in morphology and outcrop occurrence. The samples from the North and South Massifs

Relationships

PRELIMINARY GEOLOGIC INVESTIGATION OF THE LANDING SITE

6-33

FIGURE 6-39.-Glass-coated coarse-grained gabbroic rock (sample 78236) from shock-fluted, roiled boulder at station 8. The cube is 1 cm on the edge (S-73-15394). FIGURE 6-38.-Basalt f_agment (sample 78135) collected from beside a hard boulder at station 8. The cube is 1 em on the edge (S-73-15003). are strikingly similar breccias. The Sculptured Hills, in this region at least, are notably different in their greater dissection, lower slopes, and lack of large boulders. These features in combination with the limited sample suite suggest that the Sculptured Hills are underlain by less coherent breccias than the massifs. They do seem to have more sJope debris deposited at their base and a greater possibility of contamination from the thinly mantling dark material above and below the sample area. If the Sculptured Hills reflect a different structural histo_2¢ than the massifs, no evidence was developed during the mission to demonstrate it. Outcrops on the North Massif occur on the upper two-thirds (1000 m) of the slope. On the South Massif, only the upper one-third (700 m) of the slope has exposed blocks. Sampled boulders are thought to represent the uppermost part of the South Massif and the lower one-third of the North Massif. Hence, two distinct stratigrapkic levels may have been sampled. However, rocks collected from the North and South Massifs closely resemble each other in many respects, 1. Vuggy greenish-gray breccias from both massifs are similar except that cavities in rock samples from station 2 are smaller than those from station 6. 2. Greenish-gray breccias that lack cavities occur on both massifs. 3. Blue-gray breceias are identical, at least insofar as can be determined with the binocular microscope. In both places, these rocks have small proportions of white clasts and have fine-grained to aphanitic matrices. 4. Light-gray breccias from both massifs are also similar; although, as a class, these rocks are variable. The characteristics of friable matrices, dominance of dark- over light-colored clasts, and local occurrences of foliation are shared by samples from both massifs. Subordinate features of the breccias are also similar in the samples from the North and South Massifs: (1) brown pyroxene4ined rugs occur in rocks from both areas, although they are much better developed in the North Massif samples; (2) rare blue-gray breccias with vesicles were returned from stations 2 and 6; and (3) rare breccias with abundant honey-brown mineral and distinctive dark-gray mineral clasts were found at stations 3 and 7. Significant differences include the virtual lack of large light-colored clasts and prominent vesicles from the boulders studied at the South Massif. Both these features are found in the North Massif boulder samples; in addition, the station 7 boulder has dikes of blue-gray material injecting a large clast. Minor differences between the North and South Massif

breccias include: (1) vuggy metaclastic clasts occur oniy in station 2 breccias; (2) light-gray breccia at station 2 occurs as a large boulder, whereas light-gray breccias from the North Massif are known only as subordinate inclusions in station 6 boulders; and (3) many friable cataclasites were returned from the North Massif. The similarity of the rock types between the North and South Massifs suggests that the samples may represent only one stratigraphic unit. The greenish-gray breccia, light-gray breccia, and blue-gray breccia, seen as discrete boulders at station 2, are all

components of the same boulder at station 6. This evidence indicates that they may come from a single unit in the South Massif. There apparently is an unsampled type of dark rock that occurs high on the North Massif. It may represent a layer or lenses in the upper part of the massif. The foliated and layered breccia (station 2, boulder 1) is different and probably represents the capping blue-gray unit of the South Massif that was recognized in the field by the crew. Boulder 2 at station 2 appeared to the crew to resemble the tan-gray unit that underlies the bluegray unit of the South Massif.

Field Occurrence Subfioor basalts occur in the dark portions of the valley floor both as scattered blocks and fragments and as concentrations of blocks on the walls and rims of the larger craters. The areas in which the basalts were most thoroughly sampled were on the rims of Shorty and Camelot Craters, in the LM/ALSEP/SEP area, and at station 1. Several varieties of basalt were described on the lunar surface. The predominant types were coarsegrained, vesicular, relatively light-colored basalts cornposed of clinopyroxene, ilmenite, and 30 to 40 percent plagioclase. Vesicles as large as _ 1 cm in diameter typically comprised 10 to 15 percent of these rocks. In some rocks, planar partings paralleled bands expressed as differing concentrations of vesicles. Finer-grained and less vesicular varieties of basalt were recognized locally. Sherry Crater.-Subfloor basalts were sampled on the rim crest of Shorty Crater in the vicinity of a 5-m boulder (fig. 6-41). Debris that may have been shed from the boulder lies on the nearby surface, and blocks are abundant on this part of the inner crater wall. All the rocks examined were basalts that are

knobby surfaces that resemble the surfaces of terrestrial flow breccias. Shorty Crater is 110 m in diameter and is most probably a young impact crater. Its blocky floor is _ 10 to 15 m below the general surface level near the crater, and its walls are largely composed of relatively fine fragmental material. Tile impacting projectile should have encountered hard rock at a depth of no less than 10 to 15 m, and ejecta was therefore excavated from depths no greater than _ 20 m (approximately one-fifth crater diameter). It is possible that basalt fragments on the crater rim may be ejecta derived from within the upper 5 to 10 m of bedrock of the subfloor basalt unit at the Shorty site. An alternative interpretation is that coherent bedrock was not excavated by Shorty and that the basalt fragments on its rim are blocks ejected from preShorty regolith. Camelot Crater.-Subfloor basalts were collected from the rim of the large (650 m) crater Camelot. The blocks, which are partly buried by soil, are exposed near and along the low, rounded rim crest of the crater and extend downward into the crater walls (fig. 6-42) where, as in other craters, blocks are abundant. Outward from the rim crest, the block population decreases rapidly within a few meters. Within the block field, individual rocks, varying from cobble to boulder size, are subrouuded to

6-42.-Northqooking showing tabular basalt wall of Camelot large block in

photograph boulders

of part on

of station rim is banding (AS17-145-

southwest

and inner visible in

Crater. Prominent right near field

20990).

22178).

6-36

APOLLO 17 PRELIMINARY SCIENCE REPORT SEP area. The crew described the rocks as uniform, coarse, vesicular, porphyritic, clinopyroxene-bearing basalts with --_30 to 40 percent plagioclase and with ilmenite platelets in the rugs and vesicles. Vesicles commonly make up 10 to 15 percent of rock surfaces. A foliated effect is created by partings that parallel bands of differing vesicle concentration. The rocks are commonly fractured. A single set of parallel fractures is visible in one boulder (fig. 6-44), whereas so-called "Geophone Rock" is intricately fractured (fig. 6-45). Blocks in the LM/ALSEP/SEP area belong to a population of boulders that project through the dark floor material throughout the area east of Camelot Crater. Scarcity of such boulders west of Camelot suggests that the boulders near the LM are probably not Camelot ejecta but rather ejecta from the craters east of the LM in the central cluster. Station /.-Station 1 is located on the northwestern flank of Steno Crater _- 150 m from the Steno rim crest. Subfloor basalt was collected as small fragments from the soil and as chips from two vesicular 0.5-m boulders on the rim of a 10-m crater (fig. 6-46). As at Camelot Crater, the large boulders are bounded in part by tabular faces and contain parallel parting planes. A distinct planar boundary between coarsely vesicular basalt and finely vesicular basalt is oblique to a set of parallel fractures in one of the boulders.

subangular, are moderately to deeply buried, and cover _ 30 percent of the surface. The rocks tend to be tabular in shape (fig. 6-42) and no doubt preferentially broke along the well-developed set of partings (fig. 6-43). The partings parallel bands formed by variations in vesicle concentration. Descriptions by the crew indicated that the rocks were predominantly coarse-grained, subophitic, pyroxene-bearing basalts with shiny ilmenite platelets in the vugs and vesicles, The rocks appear to be notably uniform except for gray zones that may represent finer-grained or nonvesicular areas. The large basalt blocks on the Camelot rim undoubtedly represent ejecta from the crater. Impact theory suggests that the stratigraphically lowest target materials will most probably be located in the ejecta nearest the crater rim and that the maximum depth from which material is likely to be excavated is approximately one-fifth crater diameter-130m deep in the case of Camelot. However, the crater is old, and the rim has been eroded. The rocks sampled may not, therefore, represent the uppermost part of the original ejecta, and 130 m should be regarded as the maximum possible depth of their origin. LM/ALSEP/SEP area.-Large boulders of subfloor basalt were observed and sampled in the LM/ALSEP/

blocks from Steno Crater. upper 2 m of the ejecta within the Steno Crater is 600 m in blanket of diameter; the maximum depth from which rocks might have been excavated in the Steno impact is 120 m. The sampled blocks occur approximately one-fourth crater diameter from the Steno rim, however, and probably were derived from some intermediate depth in the Steno target.

6-38

APOLLO 17 PRELIMINARY SCIENCE REPORT Vesicular fine-grained basalts are characterized by a high proportion of wags and vesicles with ilmeniterich linings and by a groundmass grain size ranging from 0.3 to 0.6 ram. Olivine is commonly present in rocks of this class as microphenocrysts in amounts of 1 to 2 percent. These rocks are characterized by vug and vesicle abundances of more than 30 percent; some are frothy. Sample 71055 is a typical example of this class of basalts. Dense aphanitic basalts are characterized by their very low abundance of cavities and their extremely fine grain size. Olivine microphenocrysts are widely represented but not abundant. The average grain size of these rocks is _ 0.1 to 0.2 ram. Sample 70215 is typical of this class ofbasalts. Vesicular aphanitic basalts are characterized by abundant and exceptionally large cavities and very fine grain size. Small amounts of olivine are present in some samples. Vugs are commonly as large as a centimeter and reach 3 to 4 cm. Sample 74235 typifies this group. It is possible that the two coarse-grained basalt types are gradationally related by decrease of porphyritic pyroxene-ilmenite aggregates, but our best judyment at present is that they represent separate flow units. It seems more likely that the vesicular finegrained basalts are gradationally related to the vesicular aphanitic basalts through decrease in grain size and increase in vesicle size. The dense aphanitic basalts seem clearly to be fragments of a separate flow unit. A few samples cannot at present be fitted into these five categories. Samples 71549, 71557, and 71568 are coarse-grained basalts, but we cannot at present say whether or not they are porphyritic. Sample 71597 contains 20 to 25 percent olivinemore than any other basalt in the Apollo 17 collection. Stratigraphy A classification of basalts by type and Lunar Receiving Laboratory (LRL) number is summarized in table 6-IV. Station numbers are implicit in LRL numbers. (LRV samples are given the station number to which the LRV was proceeding when the sample was taken.) As evidenced by table 6-1V, the five basalt types have a fairly wide distribution over the traverse area. It is also apparent that the distribution is asymmetric in detail: for example, only one coarse-grained basalt was collected at station 4, and no fine-grained types were collected at station 5.

Individual samples of types (1) and (2) were generally termed "vesicular gabbro" by the Apollo 17 crew. Examples of (3), (4), and (5) were described as "fine-grained basalt," "basalt," and "obsidian," respectively, Rocks called vesicular, porphyritic, coarse-grained basalts are characterized by 3- to 4-mm, blocky, pyroxene-ilmenite intergrowths that are present in amounts ranging from 5 to 15 percent in the basalts of this class. Olivine is present in trace amounts in some of these rocks; where present, it commonly occurs as partially reacted cores in the pyroxene phenocrysts. The ilmenite content, while high for mare basalts as a whole, is relatively low compared to other Apollo 17 basalts and averages between 15 and 20 percent. The plagioclasecontentaverages25 to35 percent. Some layering occurs in larger hand samples: in one case, grain-size variations are noted; in others, feldspar and ilmenite laths are alternately foliated and randomly oriented. Vugs are more common than vesicles, although both may be present in the same rock. Cavity content is variable but averages 10 to 15 percent; vugs are alined in planes, are clearly elongate, and are layered by abundance. Sample 70035 is a typical example of this class ofbasalts, Vesicular coarse-grained basalts are very similar to those of the above class except that they lack the pyroxene-ilmenite phenocrysts, and their average grain size tends to be somewhat finer (_ 1.0 ram). This class ofbasalts is typified by sample 75055.

aRake samples 71549, 7L557, 71.568, and 71597 not classified at this time. (?) indicates questionable classification. bLoose rock > 5 cm. cChip from large boulder. dSmall fragment 1 to 5 cm. eRake sample. Because large blocks are less likely to have been reworked than small ones, the general relation of basalt fragments to their source craters is probably better established from the larger blocks. The basalts listed in table 6-1V are therefore subdivided on the basis of whether they were collected from sizable blocks, whether they were loose rocks on the surface, or whether they were collected as small fragments in soil or rake samples. Sample distribution by size and by classification type for all basalts examined to date is plotted on a traverse map (fig. 6-47). As shown in figure 6-47, large blocks were sampled only on the rims of Shorty and Camelot Craters, in the LM/ALSEP/SEP area, and at station 1. Large blocks can be confidently related to specific source craters only at Camelot and station 1, where some limits on depth of origin can be inferred. In general, the small fragments appear widely mixed, and their distribution seems to have little stratigrapkic significance. The large blocks on the rim of Camelot Crater are, so far as we know, all composed of vesicular

coarse-grained basalt. The maximum depth from which the basalt boulders on its rim were excavated is --_ 130 m. Vesicular coarse-grained basalt, represented by Camelot rim ejecta, may be the deepest subfloor material sampled on the mission, and the contact between vesicular coarse-grained material and the

next shallower unit may be at some depth < 130 m. At station 1, which lies approximately one-fourth crater diameter out on the flank of Steno Crater, the larger blocks and most of the loose rocks larger than 5 cm in diameter are of vesicular fine-grained basalt. The station is within the mappable continuous ejecta

PRELIMINARY GEOLOGIC INVESTIGATION OF THE LANDING SITE of Steno. If these are original Steno ejecta, material from intermediate depths (< 120 m) could be expected in that part of the ejecta blanket, In the LM/ALSEP/SEP area, the large blocks are vesicular, porphyritic, coarse-grained basalts. They belong to the population of large blocks that characterized the central cluster ejecta (see section entitled "Regolith and Mantle Units of the Valley Floor"). Those in the LM area are difficult to relate to the continuous ejecta of any single crater and may, in fact, represent rays or ballistic ejecta from one or more central cluster craters. If so, they could have been derived from any depth within the sequence penetrated by the central cluster craters. The largest craters are _ 600 m in diameter; hence, maximum sampling depth is _ 120 m (one-fifth crater diameter). If this rock type intergrades with the vesicular coarse-grained basalt sampled at Camelot, it probably comes from a slightly higher stratigraphic level, Except for the intensely fractured 5-rn boulder at Shorty, which is vesicular, porphyritic, coarse-grained basalt, all fragments collected there are of dense aphanitic or vesicular aphanitic basalt. If the interpretation that the coarse basalts are related is correct, the large 5-m boulder may have been reexcavated by Shorty Crater from the ejecta of some older large crater. The absence of this basalt among the other fragments that were collected at Shorty also suggests that it does not represent the upper part of the local bedrock, whereas the exclusive concentration of aphanitic basalt fragments suggests that [hese may indeed represent shallow bedrock, Sampled subfloor basalts were most probably derived from depths between --_20 and 130 m. The stratigraphically lowest basalt unit is interpreted to be the vesicular coarse-grained basalt sampled at the Camelot rim. This unit may grade upward into the coarse-grained porphyritic type sampled in the LM/ ALSEP/SEP area. The next stratigraphic unit, proceeding upward, is the vesicular fine-grained basalt represented in the Steno ejecta, and the aphanitic basalts of the Shorty ejecta may be the shallowest recognizable types. It should be stressed that this stratigraphic succession is speculative,

6-41

suggest that the graben floor is overlain by t km or more of high-density material (secs. 10 and 13). The sampled part of the subfloor basalt is interpreted to represent the upper part of the high-density grabenfilling material, which may consist entirely of basalt. Radiometric age determinations (ref. 6-6) suggest that f'dling of the valley by lava flows may have been completed by approximately 3.8 billion years ago. Before the final accumulation of the Serenitatis mare _l, broad arching east of the Serenitatis basin tilted the subfloor lavas to the east as shown in the present 1° eastward tilt of the valley floor.

Highlands

Regolith

and Surficial

Deposits

Origin The landing site valley is interpreted to be a deep graben formed at the time of the Serenitatis impact event. Geophysical data collected during the mission

The formation of a regolith of impact-generated debris has been a continuous process in the highlands of the Taurus-Littrow area as elsewhere on the Moon. The amount of regolith formed on any surface is porportional to the length of time that the surface has been exposed to bombardment by impacting bodies, whereas the thickness of regolith now present is also a function of the rate of removal of the loosened debris. Theoretically, there is no net loss of debris on flat surfaces because the debris ejected from a point of impact is balanced by the influx of debris front nearby and distant impacts. On slopes, there is a net loss of regolith as impacts at lower levels fail to throw balancing amounts of debris to the higher levels. Such a net loss of debris, sufficient to expose bedrock, occurs at the lip of Rima Hadley, the Apollo 15 landing site (ref. 6-7). The rolting tops of the massifs and the Sculptured Hills are considered very old surfaces with thick accumulations of regolith. On the generally flat surface above the Sculptured Hills, in particular, very thick regolith is implied by the close spacing of the many large craters. The regolith there is probably several tens of meters thick. The upper slopes of the massifs are nearly free of regolith as shown by exposures of bouldery zones that may represent near-surface bedrock. Such zones occur on the upper one-third of the South Massif, high on the East Massif, and on the upper two-thirds of the North Massif. These zones seem to have been the sources of most of the large boulders now resting lower on the slopes as indicated by boulder tracks. The slope of the Sculptured Hills just above station 8 is either mostly covered with thick regolith or is

6-42

APOLLO 17 PRELIMINARY SCIENCE REPORT Probably the oversteepened, already fragmented rock debris started moving immediately to fill enough of the crater to reestablish equilibrium at the angle of repose. Except for a few boulders with enough energy to climb slightly up the opposing slope of the north wall of Nansen, the debris merely slid into the crater but did not cross it. The present appearance of the massif slope into Nansen is that of an active talus apron that is slowly continuing to fill the crater. The best documented mass movement deposit is the light mantle at the base of the South Massif, which is presumed to be a mass of debris that obtained enough kinetic energy to spread out across the valley floor for a distance of _ 6 kin. In several places, there is evidence for mass movement deposits older than the talus aprons. Subdued lobes extend from the highland slopes onto the valley floor along the base of the North Massif and along the base of the South Massif between Nansen Crater and Bear Mountain. It is possible that some of these lobes are mass movement deposits overlying the subfloor basalt. Mass movements and formation of talus deposits should date back to the earliest uplift of the massifs. If the bounding faults were, as we suppose, steeper than the angle of repose for loose fragments, there must have been a large transfer of material down the newly formed slopes until the angle of repose was reached. Thus, mass movement deposits and thick talus aprons buried by subfloor basalt are inferred to overlie the still older rocks that formed the initial floor and walls of the Taurus-Littrow valley.

composed of material so friable that boulders or bedrock ledges are rapidly disintegrated by impact, In addition to the net downslope movement of ejecta, loose material tends to roll, slide, or bounce down steep slopes in response to gravity. Such movements may be initiated by jarring due to impacts or seismic events or by oversteepening of slopes by cratering or faulting. Deposits formed by these processes are distinguished herein as surflcial deposits, Volumetrically, the most important surficial deposit is talus, a poorly sorted deposit composed of debris that has arrived essentially piece by piece at its place of deposition on the lower slopes. The boulders resting near the bases of slopes and at the ends of trails leading down the slopes are clearly visible parts of the talus. Impact fragments thrown onto the lower slopes also comprise part of the talus. At the bases of large slopes, the talus forms a continuous apron, Separate talus streaks rather than aprons are clearly visible on the inner slopes of some of the large fresh craters in the region, Other surficial deposits, denoted herein as mass movement deposits, occur as masses of debris that lie beyond the bases of the slopes. These deposits result when masses of loose debris, mostly regolith, move downslope as tumbling or sliding units driven by gravity and gather sufficient momentum to move beyond the steep slopes. These materials are cornmonly set in motion by some jarring event or when they become unstable on oversteepened slopes, Surficial deposits are undoubtedly present on the lower parts and at the bases of all the large steep slopes of the highlands. Gentle intermediate slopes near the base may reflect the occurrence of a high-lava mark of subfloor basalt. The slopes are more probably talus deposits that may have been partly redistributed valleyward by impacts: At stations2,6, and LRV-10, located on the gentle siopes immediately above the valley floor, fillets occur preferentially on the upslope sides of boulders, which indicates that debris is currently moving downslope, Along much of the base of the South Massif, the talus intersects the valley floor at a sharp angle, which suggests that downslope movements have been renewed so recently, perhaps as a consequence of recent massif uplift, that impact processes have not had time to round the knickpoint. Part of this talus deposit has filled approximately three-fourths of Nansen Crater. The Nansen impact undoubtedly caused oversteepening at the base of the talus slope,

Regolith

and Mantle

Units of the Valley

Floor

The subfioor basalt is overlain by fragmental debris that is as much as 15 m thick where it iscut by Shorty and Van Serg Craters. A complete understanding of this material must await detailed descriptions of the numerous soil and core-tube samples. Part of the material is undoubtedly impact-generated regolith similar to that developed on mare basalts elsewhere on the Moon. Premission geologic maps of the Apollo 17 site (ref. 6-1) indicated, in addition to normal regolith, light and dark mantle units. The light mantle unit was identified and sampled at stations 2, 2A, and 3 and at LRV sample stops 2, 5, and 6. The dark mantle was not recognized on the lunar surface as a distinct stratigraphic unit; a unique darkening corn-

PRELIMINARY GEOLOGIC INVESTIGATION OF THE LANDING SITE ponent, if present, is apparently intimately mixed with the impact-generated regolith, In this report, the fragmental material overlying the subfloor basalt is divided into an older regolith, information on which comes mainly fiom the Van Serg Crater ejecta, and a younger regolith that occurs at or close to the surface. In addition, major crater ejecta blankets around the central crater cluster and Shorty and Van Serg Craters are mapped and described as separate portions of the surficial debris layer. Inferred stratigraphic relationships among these units are shown in figure 6-48. Petrography of Regolith Breccias

6-43

Crater. Samples 70019 and 79175 are breccias composed of friable dark clods loosely cemented by dark glass; these also closely resemble rocks returned by earlier Apollo missions. Regolith breccias were also found at two areas marginal to the valley floor. Five small breccia fragments (78508 and 78515 to 78518) were found in a soil sample from station 8. Samples taken from SWP Crater (e.g., 78120), did not survive in pieces larger than 1 cm but appear to be similar to the other regolith breccias. Older Regolith

A total of 14 samples of breccia (70018, 70019, 70175, 71515, 72135, 79035,79115,79135,79175, 79195, 79225, 79226, 79227, and 79228) was collected from the valley floor at stations 1, 9, LM/ALSEP/SEP, and LRV-1. Most of the samples are probably soil breccias ejected from the older regolith, Some, however, such as 70019, are soil breccias formed by impacts in the younger regolith. These breccias are all dark to very dark gray, are friable to moderately coherent with numerous penetrative fractures, and typically have low clast populations, Samples 79115 and 79135 are layered, with alternating layers on the order of several centimeters thick that are distinguished by differing clast abundances. Similar layering is also visible in lunar surface photographs of breccia boulders at Van Serg Crater (fig. 6-49). Surfaces of penetrative fractures are commonly weakly slickensided, as was typical of regolith breccias returned from earlier Apollo missions. Slickensides are especially well developed in sample 79135. Clasts larger than 1 mm make up from 1 to _ 15 percent of the breccias; most clasts are smaller than 1 cm, although the crew reported clasts as large as 0.5 m in breccias of this type at Van Serg .Shorty jecta e • _ .:._,, Younger regolith Central cluster ejecta "Light antle m _--_',-Camelot ejecta'" Subfloor basalt Olderregolith

The ejecta of the 90-m-diameter Van Serg Crater includes a large proportion of soft, dark, matrix-rich breccias (figs. 6-49 and 6-50) the petrography of which is described in the preceding section. On the crater rim, the breccias contain scattered light-gray lithic clasts that are as large as _ 2 cm in diameter. Light clasts as large as 0.5 m in diameter were seen in the dark-matrix fragment-rich breccia on the crater floor. The Van Serg breccias can be interpreted as regolith materials indurated by the impact that formed Van Serg Crater. So far as we know, subfloor basalt was not excavated by the impact, although traverse gravity data (sec. 13) imply its presence in the subsurface. At least 15 m of regolith material is _

APOLLO 17 PRELIMINARY SCIENCE REPORT be that of a very complex lens as it is composed of the ejecta, rim, and continuous blanket deposits of each of the craters within the cluster. At station I, a 2-m-deep crater does not appear to have penetrated the total thickness of the unit, which is expectable because station 1 is only approximately one-fourth crater diameter out from the rim of Steno, a member of the cluster. At the deep core site, _ 40 m north of the ALSEP central station, the central cluster ejecta is assumed to be thin because the site is more than a crater diameter away from any large member of the cluster. The deep core probably penetrated the entire unit; the change of soil appearance, seen in corestem joints, at a depth of _ 1 m probably indicates the base of the central cluster ejecta. All blocks from the central cluster ejecta that were sampled are considered to be subfioor basalts. Smaller sampled fra_gnents are more difficult to relate to a source, but the preponderance of surface rock fragments from the LM/ALSEP/SEP and station 1 sites must have come from the subfloor basalt either directly or after reexcavation. Soil samples in the area must be considered as originating from the overlying younger regolith unit. The ejecta of the central cluster unit is inferred from crater depths and estimated regolith thickness to contain roughly three times as much subfloor basalt as older regolith. The older regolith contains a large percentage of fine basalt fragments, so the expected amount of basalt in the central cluster ejecta, or later reexcavated deposits, is at least 80 percent. A net effect of the central cluster ejecta was to create an immature regolith surface layer overlying what must have been, in general, a very mature regolith. The immaturity is most easily seen in the common occurrence of blocks and rock fragments. It is also reflected in the lithologic composition by the high percentage of fragments newly derived from the subfloor basalt and a little admixture of exotic components such as ejecta from impacts in the highlands. Samples collected from the central cluster ejecta, either directly from boulders protruding through the younger regolith or from reexcavated parts of the unit adjacent to some recent crater, would be expected to consist mostly of subfloor basalts that originally came from the uppermost 120 m of that unit. Younger Regolith Premission mapping of the Taurus-Littrow valley

FIGURE

6-50.-West-looking photograph showing dark matrix-rich breccia boulders on rim of Van Serg Crater. Note small white clasts in to the right of boulder and sheared aspect of boulder the foreground the gnomon

(AS17-142-21791). interpreted to have overlain the subfloor basalt in the Van Serg area when the crater was formed. The deepest part, represented by the Van Serg rim and floor rocks, is presumed older than the central cluster ejecta and hence represents older regolith material, Central Cluster Ejecta The regolith is subdivided locally by recognizing as unique a portion that is considered to be the complex ejecta blanket of a cluster of large craters that lie mostly to the south and east of the LM (fig. 6-51). This unit, distinguished by an abundance of blocks visible at the surface, is termed the central cluster ejecta. Younger deposits are apparently too thin to bury the blocks in the unit, and the unit is too young for the blocks to have been reduced much in size by later impacts. The general distribution of blocks considered as central duster ejecta is shown in figure 6-51. It is assumed that beyond a crater diameter from the nearest crater of the cluster, the fine-grained ejecta will be present in significant amounts only discontinuously. The unit probably does not extend as far as the5. LRV station at Tortilla Flat but may coat station The shape of the central cluster ejecta unit must

PRELIMINARY GEOLOGIC INVESTIGATION OF THE LANDING SITE

6-45

FIGURE 6-5l.-Map showingthe craters of the central cluster, related boulders, and the outline of the central cluster ejecta. showed the valley floor to be covered with a dark mantle unit considered younger than the subfloor basalts and older than the light mantle. With the recognition of the central cluster ejecta unit, the definition of the dark mantle must be modified. The surface layer of material that overlies the central cluster ejecta where it is present is herein considered as a unit, composed of both regolith and whatever dark mantle may be present, and is termed the younger regolith. The surface of this unit was traversed, so all shallow soil samples should be part of it. The light mantle is considered as a local unit that is equivalent to some central part of the younger regolith. Regolith younger than the central cluster ejecta is certainly present at the landing site, but a unique component that can be called dark mantle has not been identified. The reasons for having postulated a dark mantle unit during premission mapping remain valid and will be briefly stated. The findings of the Apollo 17 crew will then be summarized. An area of very low albedo is present along the southeastern edge of the Serenitatis basin as shown on full-Moon photographs (fig. 6-52). The boundaries of this area have been mapped somewhat differently by various mappers and the interpretations of the very low albedo have differed, but the presence of an anomalous area has been recognized by previous workers (refs. 6-1 and 6-2 and part B of sec. 29). Photographs taken during the Apollo 15 mission indicated that dark areas existed along the edge of

Mare Serenitatis, in the valleys to the southeast, and as spots and discontinuous coatings in the highlands, This distribution seemed to require an interpretation of a thin mantling unit that conformed to underlying topography. Several experiments seemed to confirm the presence of a dark mantle unit, especially the spectral results that indicated a compositional difference from other mare volcanic types (ref. 6-8). Because it is widespread, the dark mantle was

interpreted as most likely to be a volcanic pyroelastic deposit with many source vents located both in the highlands and in the valleys. The thickness was considered to range from as much as 20 m to as little as a few centimeters within the traverse area planned for the Apollo 17 crew. The reasons for the existence of a dark mantling unit are discussed in detail in part B of section 29. The photographs taken from orbit during the

PRELIMINARY GEOLOGIC INVESTIGATION OF THE LANDING SITE Apollo 17 mission permit a reevaluation of the very-low-albedo area seen on the full-Moon photographs. The low Sun angles of the Apollo 17 photographs permit individual mare units to be separated. A comparison of the Apollo 17 photographs with the full-Moon photograph shows that, in the Mons Argaeus area, the dark mantle edge cuts across mare unit contacts and is thus independent of the mare units. In the Mons Argaeus area, the dark mantle apparently overlies the high-alhedo, main mare unit of Mare Serenitatis. As shown in figure 6-52, the very low albedo of the dark mantle unit extends from the Mons Argaeus area eastward to include the landing site. Hills west of the landing site, in addition to having a very low albedo, have a more rounded and subdued appearance than adjacent brighter hills as though covered by a thin mantle, In summary, the weight of evidence favors the formation of a dark mantle sometime after the deposition of the subfloor basalt in the TaurusLittrow region. Evidence that the mantle is substantially younger than the subfloor is present in one area to the west of the landing site. The dark material apparently has been mixed with underlying material into a regolith unit. The thickness of dark mantle that was suggested in premission studies ranged from several centimeters to 20 m. The 20-m thickness was based on the hypothesis that Shorty Crater bad ejected only (lark mantle from beneath light mantle. Most of the thickness at Shorty between the light mantle and subfioor basalt is now considered older regolith, and no distinct dark mantle layer was seen. If only several centimeters of dark mantle were present, it could be mixed with the regolith portion of the valley fill unit. Although no unique dark mantle component has been identified at the Apollo 17 site, the evidence for such a camponent at the edge of Mare Serenitatis seems inescapable. The low albedo may be caused by the presence of many tiny opaque black spheres found in the softs (sec. 7). New photographs from orbit reinforce other evidence for the existence of a mantling component in the Family Mountain region just a few kilometers west of the traverse route. The evidence is the presence of surface areas that appear distinctly different. On Lunar Orbiter V and Apollo 15 photographs, a triangular area, which appeared slightly out of focus or fuzzy, had been noticed between Family Mountain and the South Massif. This area includes

6-47

the cone considered as a cinder cone (ref. 6-9). On the Apollo 17 photographs taken at a low Sun angle, the area has many sharply defined small craters, but larger features are definitely more rounded in appearance than they are in adjacent areas. The best explanation seems to be that the area is a unit of mantling material of local extent. Its area might include the western edge of the light mantle. Two other small areas of smooth surfaces nearby are adjacent to steep slopes; the smoothing unit, however, could be debris derived from the nearby slopes. In general, tile areas of smooth surface are considered to be evidence for dark mantle, and their nearness to the traverse area suggests that at least a few centimeters of dark mantle might exist in the traverse area. Such a thin unit with the degree of cratering seen in the smooth areas would be gardened by impacts to a depth greater than its thickness; that is, it would not exist as a pure layer but would be mixed with underlying material into a regolith layer.

Light Mantle The light mantle is a deposit of high-albedo material with finger-like projections that extend 6 km across dark plains from the South Massif. The light mantle was interpreted from premission photographs as a probable landslide or avalanche from the steep northern slope of the South Massif (refs. 6-1 and 6-10). The samples collected at stations 2, 2A, and 3 on the light mantle are similar to those that comprise the South Massif, which supports this hypothesis (sec. 7). A cluster of apparent secondary craters that is visible on top of the South Massif in the low-Sunangle panoramic camera photographs from Apollo 17 may record the impacts that initiated the awdanche. Thirteen rock samples were collected from stations on the light mantle. Three of these samples (73155, 73217, and 73235) are blue-gray breccias with light-gray clasts and appear to be very similar to those collected at station 2. Sample 73217 is unusual in that it has a blue-gray portion of the breccia with a veneer on one edge that is composed of blue-gray and white sugary clasts in a friable light-gray matrix. The main body of this rock may be a clast from light-gray breccia. Two samples (73215 and 73255) are lightgray breccias composed of gray clasts in a light-gray friable matrix and appear to be very similar to those sampled from boulder 1 at station 2. Sample 73215 has a crude foliation resulting from alternating bands

6-48

APOLLO 17 PRELIMINARY SCIENCE REPORT

of gray and white material. Three samples (73216, 73218, and 73275) are greenish-gray breccias and appear to be similar to those collected from boulder 2 at station 2. Five samples collected at LRV-6 (74115 to 74119) are very friable, medium light-gray regolith breccias that contain a few white clasts. The materials of the light mantle have an albedo of 20 percent at the surface, which is slightly lower than the 25 percent of the massif slopes (see section entitled "Albedo Measurements"). This albedo difference is probably due to the formation of a regolith and consequent darkening of the surface of the light mantle; continued downslope movement of materials of the South Massif brings newly exposed materials to the surface of the massif, hence the darkening process is not so effective on the steep slopes. At a distance, the crew recognized that the bright aspect of the light mantle is primarily manifested by numerous small craters the walls and rims of which are brighter than any in the dark plains. These craters probably expose fresh material. The light mantle consists mainly of unconsolidated fines. Comments by the crew and photographs taken at stations 2A and 3 and while driving indicate that rocks > 25 cm across are sparse on the surface of the unit. Smaller rocks are fairly common but not abundant. A single large (3 to 4 m) boulder was encountered on the traverse. The scarcity of rocks suggests that the avalanche mainly consisted of regolith from the surface of the massif and did not involve the sliding of underlying bedrock, The light mantle feathers out at its margins away from the South Massif. Near the extremities of the mantle, Shorty Crater and a smaller nearby crater appear to penetrate through the slide into underlying valley regolith. Craters of this size nearer the South Massif do not penetrate to darker underlying material. A greater thickness near the base of the massif is also suggested by the occurrence of numerous low ridges that become less distinct farther from the massif (fig. 6-53). The ridges are alined in the apparent direction of movement of the avalanche away from the massif and are spaced 25 to 100 m apart. In some orbital photographs, lineaments appear to form V's that open away from the massif. Similar lineament patterns are visible in areas of similar relief just northwest of the light mantle. This similarity suggests that the V lineaments are not necessarily associated with the emplacement of the avalanche,

The lineaments may be enhanced or created by the lighting condition, an effect that is not fully understood (refs. 6-11 and 6-12). On the other hand, the lineament patterns resemble interference patterns seen in the lee of obstacles in a moving fluid. Descriptions by the crew at station 2A indicate that the upper portion of the light mantle is composed of 5 to 15 cm of medium-gray material underlain by light-gray material. The medium-gray material may be regolith, darkened by the formation of impact glass, that has been formed from small contributions of dark soil from impacts occurring on the dark portions of the valley floor. The trench (fig. 6-54) at station 3 was dug into the rim of a 10-m crater. The bottom of the trench exposed a marbled zone of light- and medium-gray materials. The texture of the marbled material is similar to the textures and ejecta from terrestrial impacts such as Meteor Crater (fig. 6-55), and this material may be ejecta from the 10-m crater in which undiluted light mantle was mixed with precrater regolith. Overlying the marbled material is a 3-cmthick layer of light material, which may represent unmixed light mantle ejected from well below the precrater regolith. Where the trench was dug, on the rim of the 10-m crater, the upper part of the stratigraphic sequence had probably been eroded by impact of small meteorites (refs. 6-7 and 6-13). Thus, the 3-cm layer of light material was probably signifi-

PRELIMINARY

GEOLOGIC

INVESTIGATION

OF THE LANDING

SITE

6-49

FIGURE 6-54.-Presampling view of trench wall at station 3. (a)Southwest-looking view (ASI7-13821148). (b) Enlargement of part of figure 6-54(a). Hachured area is light-gray material; remainder is medium gray. The 0.5 cm of medium light-gray regolith that caps the mapped units is not separately mapped (AS17-138-21148).

cantly thicker at its time of deposition as crater ejecta. The uppermost layer in the trench is 0.5 cm of medium-gray material that is slightly lighter than the medium-gray component of the marbled zone. This

layer is interpreted to be the regolith that has formed on the ejecta of the 10-m crater (fig. 6-56). The size-frequency distribution and morphologies of craters on the light mantle suggest that its age is

[] FIGURE 6-55.-Marbled texture in ejecta at Meteor Crater, Arizona. Compare with figure 6-54 (U.S. Geological Survey, Center of Astrogeology photograph 76824). comparable to that of the crater Tycho, or on the order of 100 million years. Crater counts show that the saturation crater size is 2 to 4 m. The saturation crater size at Tycho is 2.8 m (ref. 6-14). Another way to estimate age uses the crater degradation model of Soderblom and Lebofsky (ref. 6-13). The diameter of the largest unshadowed crater (Dx) on Apollo 17 panoramic camera frame 2308 (Sun angle SA = 16.3 °) is 30 + 10 m. By using this calculation, the age expressed as the diameter of a crater (DL) which would be eroded to 1° slopes was calculated as 13 -+ 5 m. This age compares with that of Tycho Crater, where D L = < 20 m (reL 6-13). A minimum age for the light mantle is the exposure age (20 to 30 million years) for the orange soil deposited on the rim of Shorty Crater (ref. 6-15). The light mantle is larger than most other lunar avalanches and, unlike many, has no conspicuous source ledge on the slope above. New evidence suggests that the avalanche was triggered by secondary impacts from a distant crater. This evidence is based on the recognition on Apollo 17 low-Sun-angle orbital photographs of a cluster of 100-m craters on the top of the South Massif and a similar cluster on the plains adjacent to the northwest side of the light mantle. The elongation of the cluster craters suggests that they are secondaries from a distant crater to the southwest, possibly of Tycho. If impacts from the same cluster of secondaries impacted the northwestern slope of the South Massif, they could have initiated the avalanche. Elsewhere on the Moon are []

FIGURE 6-56.-Interpretation of stratigraphy as seen in trenches on the light mantle at stations 2A and 3. other avalanches that clearly were similarly initiated by the impact of crater ejecta on slopes facing away from the primary crater (ref. 6-10)•

Shorty Crater Shorty is a fresh 110-m crater located near the north edge of the light mantle. It resembles other craters that have been interpreted as young impact craters. The floor is hummocky, with a low central mound slumps and with marginal hummocks that resemble forming discontinuous benches along the

iower parts of the crater wall. The rim is distinctly raised and is sharp in orbital views. The dark ejecta blanket is easily distinguished from the high-albedo surface of the surrounding light mantle, which it overlies. However, the low albedo of the ejecta is similar to that of the dark younger regolith elsewhere on the plains surface. Samples were collected in a low place on the rim crest of Shorty Crater just south of a 5-m boulder of fractured basalt (fig. 6-57). Debris that may have been shed from the boulder lies on the nearby surface, and blocks are abundant on this part of the inner crater wall. All the rocks examined are basalt. Most are intensely fractured and some show irregular knobby surfaces that resemble the surfaces of terrestrial flow breccias. Rocks range from angular to subrounded; some are partially buried; some are filleted, including the upslope sides of a few of the larger boulders on the inner crater wall.

PRELIMINARY GEOLOGIC INVESTIGATION OF THE LANDING SITE

6-5 1

FIGURE 6-57. Northwest-lookingview of southwest rim of Shorty Crater showing sampling area and areas of orange soil as indicafed by dashed lines. Large sampled boulder on rim is 5 m wide (AS17-137-21009and 21011). The floor material, exposed in the central mound (fig. 6-58), is blocky and extremely jagged. It may differ in lithology from the basalts of the rim. The hummocks or benches that encircle the floor as well as portions of the walls are also blocky, ttowever, the wall, the rim, and the outer flank of Shorty Crater consist largely of dark material that is much finer grained than the floor. On the crater rim, fragments as large as --_15 cm in diameter typically cover < 3 percent of the surface. Scattered coarser fragments, ranging up to at least 5 m in diameter, are present. The crater rim and flanks are pitted by scattered, small (to several meters) craters the rhns of which range from sharp to subdued. Typically, their ejecta are no blockier, except for clods, than the adjacent surfaces. Although a volcanic origin has been considered for Shorty Crater, no compelling data to support the volcanic hypothesis have been recognized. The type of pure accumulation of basaltic spatter or cinders that forms steep-sided terrestrial volcanic cones has not been recognized; nor does the steeply raised sharp rim of Shorty resemble the low rounded rims of terrestrial maar craters. Most probably, Shorty is an impact crater. Its blocky floor may represent either impact-indurated soil breccia or the top of the subfloor basalt, which is buried by 10 to 15 m of poorly consolidated regolith, including light mantle (fig. 6-59). The predominantly fine-grained wall, rim, and flank materials are probably ejecta derived largely from materials above the subfloor, and the basalt blocks may be ejecta derived from the subfloor, Regardless of its origin, the crater is clearly younger than the light mantle, FIGURE 6-58.-North view across 110-m-diameter Shorty Crater. Far crater wall, blocky benches encircling floor, and jagged rocks of central mound are visible (AS17-13721001).

FIGURE 6-59.-Schematic cross section through Shorty Crater with vertical scale exaggerated. Unusual orange soil is known to occur in two places on the Shorty Crater rim crest as well as in the ejecta of a small fresh crater high on the northwest interior wall of Shorty (fig. 6-57). A trench exposed an 80-fro-wide orange zone that trends parallel to the crater rim crest for several meters. The orange soil is markedly coherent as shown by the systematic fractures in the trench wall (fig. 6-60). It is also zoned; a wide central reddish zone, now known to consist largely of small red and orange glass spheres and fragments, grades laterally to marginal yellowish zones _ 10 cm wide (fig. 6-61). J'he yellowish zones in turn are in sharp steep contact with light-gray fragmental material that is probably typical of the Shorty Crater rim. A double drive tube placed in the axial portion of the colored zone bottomed in black fine-grained material now known to consist of tiny, opaque, black spheres (sec. 7). The contact between orange and black glass occurs within the upper drive

6-52

APOLLO

17 PRELIMINARY

SCIENCE

REPORT

FIGURE 6-60.-North-looking photograph showing orange glass material and light-gray fragmental material exposed in trench on rim crest of Shorty Crater. Short lines indicate more prominent fractures in the orange glass material (AS17-137-20986). tube at a depth estimated from the debris smeared on the exterior of the tube to be _ 25 cm. The origin of the red and black glass materials is uncertain. The radiometric age determination for the orange glass material implies solidification during or shortly after the period of subfloor basalt volcanism. Shorty Crater, of course, is much younger. Such glass, whether ejected from an impact crater or a volcanic

material may represent the regolith that has formed since the formation of Shorty Crater. Serg Crater

1-

Yellowish Light-gray 70 fragmental cm material

, \

._ Yellowish Bottomftrench o

Van Serg is a fresh 90-m-diameter impact crater. It has a blocky central mound _ 30 m across, discontinuous benches on the inner walls, and a raised blocky rim with a distinct crest from which the blocky ejecta blanket slopes outward. The bench is particularly well that materials in the crater wall above the bench were darker than those below. Its ejecta blanket is distinct in lunar surface views because of its blockiness, which is greater than the north the adjacent the crew reported developed on that of wall, where plains. The ejecta blanket can be recognized, at least in part, in orbital photographs as a distinct topographic feature, but it is inseparable from the adjacent plains on the basis of albedo. Rocks in the Van Serg ejecta range to -_ 30 cm, with a few boulders as large as 1 to 2 m in diameter. At the rim crest, fragments larger than 2 cm cover _ 10 percent of the surface, but they cover no more than 3 percent of the surface on the outer flank of the crater. The predominant rock type at station 9 is soft or friable dark matrix-rich breccia. White clasts ranging to ,-_2 cm in diameter are visible in some rocks on the crater rim, and light-colored clasts possibly as large as 0.5 m in diameter were seen in rocks of the central mound. Some rocks are slabby. Closely spaced, platy fractures occur in some, and a few show distinct alternating light and dark bands. Some frothy glass agglutinate was also sampled. Despite their apparent softness, the rocks are typitally angular. Many are partially buried, but there is little or no development of fillets even on the steep inner walls of Van Serg Crater. Soil at the surface is uniformly fine and gray with no visible linear patterns. The uppermost 1 or 2 cm is loose and soft. A trench on the outer flank of the crater exposed _ 10 cm of light-gray fragmental material below a 7-cm layer of dark surface material (fig. 6-62). Craters younger than Van Serg are extremely rare in the station 9 area. A few small (_ 1 m) craters are present. A large subdued depression immediately south of Van Serg may be an old crater now mantled by Van Serg ejecta. The frequency and angularity of blocks, the paucity of craters, the general absence of t'dlets, and the uneroded nature of the crater rim and

vent, may have lain as a layer (or layers) either within the upper part of the subfloor basalt sequence or deep within the regolith overlying the sub floor basalt in the target area. If so, the orange and black glassy materials may represent clods of ejecta excavated by the Shorty impact. However, the symmetrical color zonation of the orange soil, internal color zoning of at least one clod, and apparent paralMism of the steep boundaries of the zone with both the internal color banding and the axis of the rim crest are improbable features for a clod of ejecta unless the clod has undergone alteration subsequent to its emplacement, a process heretofore unknown on the Moon. The color zoning and steep contacts might be more readily explained if the glass material, derived from a layer of similar material in the target, were mobilized by the impact and driven dike-like into concentric fractures. However, the occurrence of black glass material below the orange glass material in the double drive tube (fig. 6-61) and the absence of the black glass at the surface suggests the existence of horizontal or gently dipping layering, a geometric arrangement that would be reasonable in a clod of ejecta but is difficult to reconcile with injection of old glass material into a concentric fracture, A 0.5-cm-thick layer of dark fine-grained soil overlies both the orange soil zone and the adjacent light-gray fragmental material. This dark surface

The valley in which Apollo 17 landed is bounded by high steep-sided mountain blocks that form part of the mountainous eastern rim of the Serenitatis basin. The blocks are thought to be bounded by high-angle faults that are largely radial and concentric to the Serenitatis basin. Hence, the valley itself is interpreted as a graben formed at the time of the Serenitatis impact. Some of the prominent faults are not concentric or radial to Serenitatis, although major displacements probably occurred along them when preexisting zones of weakness related to older basins Serenitatis was formed. The faults may have been such as Tranquillitatis or to the so-called lunar grid. Massifs and Sculptured Hills

Dark surface material overlieslight-gray fragmental material (AS17-142-21827). the central mound attest to the extreme youth of Van Serg Crater. Evidence for its being younger than Shorty is equivocal. Its rim seems to be slightly sharper than the rim of Shorty in orbital photographs, and small craters may be slightly more abundant on the Shorty rim. There is no evidence that the Van Serg impact excavated subfloor basalt. The fragment-rich breccias and dark matrix-rich breccias of its floor, rim, and outer flank may be regolith breccias indurated in the Van Serg impact. If this reasoning is correct, then at least 15 m of regolith is inferred to overlie the subfloor basalt in the Van Serg area. However, these breccias may be of a volcanic type not previously recognized and may be associated with the orange and black glass formations. Near coincidence of the albedos of the blocky Van Serg ejecta blanket and the nearby smooth regolith surface is puzzling. Possible explanations are that the elusive dark mantle material is represented in the ejected older regolith as well as at the present regolith surface or that the dark surface material recognized on the crater rim and flank has masked any distinction between the Van Serg ejecta and the nearby undisturbed regolith surface,

Each massif block probably is a stmctural entity uplifted during the Serenitatis event. Rejuvenation of these older structural elements may have occurred during the Imbrian event as suggested by the elongation of the Taurus-Littrow valley, which is radial to both Imbrium and Serenitatis. Segmentation of the massifs may be an inheritance from the even earlier Tranquillitatis event. The massifs adjacent to the landing site appear similar in slope, albedo, and degree of cratering. They contrast with the closely spaced domical hills of the Sculptured Hills, which also form fault block mountains. No unequivocal Sculptured Hills material has been recognized among the samples; hence, the reason for the differing appearances of the massifs and the Sculptured Hills is not clearly understood. The massifs may consist of distinctly different materials with more friable material occurring in the Sculptured Hills. For example, the massifs may consist largely of pre-Serenitatis ejecta uplifted in the Serenitatis event, whereas the Sculptured Hills may consist mainly of Serenitatis ejecta. Alternatively, each might consist mainly of a different facies of Serenitatis ejecta, with more thorough recrystallization increasing the coherence of the massif materials. On the other hand, the initial materials of the two units may be similar, but subsequent deformational history may have caused their different aspects. For example, relatively recent uplift selectively affecting the massif blocks may have rejuvenated slope proces-

PRELIMINARY GEOLOGIC INVESTIGATION OF THE LANDING SITE ses to create the relatively uninterrupted steep slopes that distinguish the massifs from the Sculptured Hills. Single, major bounding faults are inferred along the face of each mountain block. Such faults can be recognized at younger, less modified basin margins (e.g., Orientale, Imbrium). These faults are probably very steep more than 60 ° and probably close to 90 ° tbr the radial faults. They are buried under the talus aprons and lie valleyward from the lowest outcrops visible on the massif faces. Sharp knickpoints at the massif bases suggest that additional later uplift may have reinitiated downslope movement of talus. Valley The Taurus-Littrow valley appears to be a long narrow graben radial to the Serenitatis basin. The graben probably is composed of several structural blocks and did not move as an entity. Its floor, now buried, is thus visualized as having steps between blocks the separate tops of which are at different elevations. These buried tops probably resemble in roughness the present tops of the massifs and the Sculptured Hills. The present uniformity of the valley floor is due to the continuity of the valley f'dl surface. The fill probably consists of rubble created al the time of block faulting overlain by basalt (subfloor) and regolith materials that are younger than any large differential movements of the structural blocks. The surface continuity must be due mainly to infilling by subfloor basalts that are interpreted frmn geophysical measurements (secs. 10 and 13) to be 1 km or more thick. The valley floor slopes _ 1° toward its eastern end. This small dip is interpreted as structural rather than depositional because it is coincident with other regional surface slopes. The NASA Lunar Topographic Orthophoto Map (1972) shows an east-tilted belt that includes the Taurus-Littrow valley and the floor of the crater Littrow (fig. 6-1). The tilt is interpreted to record development of a broad arch formed by uplift along the mountainous Serenitatis rim after the subfloor basalt fill had accumulated in the Taurus-Littrow graben. Long shallow grabens largely concentric to the Serenitatis basin were created during this deformation. They were truncated by younger mare-filling deposits that subsequently accumulated in the Serenitatis basin,

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Younger deformational features on the valley floor include the Lee-Lincoln Scarp, which is discussed subsequently and several small sharp grooves that are visible on the surface of the light mantle in the low-Sun-angle photographs taken with the Apollo 17 panoramic camera. These grooves appear to be small grabens similar to the small graben rllles that are common on mare surfaces. They were probably formed by minor tectonic movements that occurred after the emplacement of the light mantle. Lee-Lincoln Scarp

The origin and nature of the Lee-Lincoln Scarp are still puzzling. Its steep face nearly everywhere faces east, commonly in a pair of steps the total relief of which reaches 80 m in the center of the valley. A few prominent smaller west-facing scarps are present, best seen from Lara Crater northward where the shadowed highlighting is enhanced by the whiteness of the light mantle (fig. 6-53). Individual segments disappear along strike as another picks up the displacement; in places, it appears almost braided. The trends of individual segments of the scarp appear to alternate between north and northwest as if controlled by an underlying prismatic fracture system. This same set of trends is identifiable in segments of the scarp along the western base of the North Massif. Here, however, the scarp is single and always faces east-toward the massif-in the form of a reverse or thrust fault. Forty kilometers to the north, the scarp passes out onto the dark plains surface where it cuts Rima Littrow I (fig. 6-1). The overall length, trend, asymmetry, and morphologic character of the scarp resemble that of the larger wrinkle ridges of the adjacent Serenitatis mare (part A of sec. 29). This similarity suggests a common origin-possibly folding and thrusting of a thin plate (ddcollement sheet) eastward. The relative youth of this deformation is indicated by the transection of fresh Copernican craters by wrinkle ridges in the mare, by the fresh, possibly rejuvenated scarplets that may be younger than the light mantle, and by the good preservation of the scarp in the unconsolidated materials of the North Massif face. An alternative possibility is that the Lee-Lincoln Scarp is the surface trace of a complex high-angle fault that changes strike where it follows the old North Massif boundary fault immediately north of the valley.

6-56 ALBEDO

APOLLO 17 PRELIMINARY SCIENCE REPORT MEASUREMENTS of the South Massif (depicted by unit 5) seems to be as narrow as along the northern side of the valley floor. The massifs and hills surrounding the valley generally have albedos ranging from 15 to 34 percent, as is normal for lunar highlands. However, local small depressions contain dark material with albedo as low as 10 percent. The lightest regolith material occurs on the steepest slopes and on top of some rounded domes. The slopes of the South Massif are lightest from one-fourth to three-fourths of the way down the slope front and darker near the top and bottom of the slopes. The small undulating plains area on top of the South Massif (unit 5) is as dark as the valley floor between the massif and Family Mountain (14 percent) with tongues of the material draping over the edge of the upper massif slopes and extending down the steeper slopes. The North Massif has lighter regolith on the tops of rounded domes and down the upper two-thirds of the slopes. Small closed depressions on top of the massif that are too small to be shown in figure 6-63 show slight darkening in the western part and increasing darkening toward the eastern part. The Sculptured Hills show a general darkening toward the east with the regolith in similar small depressions ranging in albedo from 17 to 14 percent. The large upland basin to the northeast has extensive regolith with 12-percent albedo. The East Massif is similar to the North Massif, but the small closed depressions darken toward fire southeast. Albedos as low as 10 percent occur immediately south of the map area. The surfaces of the small intramassif and intrahill depressions are from t200 to 2000 m higher than the floor of the Taurus-Littrow valley. These dark areas are considered to contain bedrock material similar to the surrounding massif or hill bedrock. There is no observed geologic evidence to suggest that any marelike basalt could have flooded these small depressions. Yet the darker albedos of many depressions are similar to the albedos of the mare areas and of the Taurus-Littrow valley floor. The lunar regolith is generally considered to be developed primarily by repetitive crushing of local bedrock by impact processes (ref. 6-17). The product is a fine-grained layer that is darker than the original bedrock. Mare basalt fragments with albedos ranging from 13 to 21 percent occur with free-grained regolith of 9- to 13-percent albedos (ref. 6-7). The ratio of the albedo of the fine-grained regolith to the

Lunar surface and orbital photographs were used to map albedo in the Taurus-Littrowarea. Down-Sun 60-mm photographs at each traverse station in cornbination with high-resolution 500-mm photographs of the mountain slopes provided the control for photometric measurements made from orbital photographs, Relative f'dm densities of Apollo 15 panoramic camera frames 9557 and 9559 were measured on a Joyce-Loebl microdensitometer. The scanning aperture was 50/2m square, equivalent to an integrated 9 m 2 of lunar surface. Film densities, after calibration to normal albedo as determined in down-Sun lunar surface photographs in areas of fine-grained regolith and after adjustment to remove the effects of topographic slopes, are proportional to albedos of lunar surface materials. Topographic corrections were derived from the NASA preliminary topographic map of part of the Littrow region of the Moon. The resulting map (fig. 6-63) was smoothed to remove scanning noise and high-frequency albedo variations. Important qualifications are that the usual lunar photometric function was applied for the Apollo 17 areas and that the albedo adjustments for topography are approximate because of inaccuracies of slope orientations. Comparisons of albedo values are most reliable between areas with similarly oriented slopes. The albedo map (fig. 6-63) can be compared with an orbital photograph of the area at a similar scale (fig. 6-64). The east-west trending valley floor is the most continuous physiographic unit. Except for the light mantle, in which albedo ranges from 14 to 23 percent, the albedo of the valley floor is low. It ranges from 14 percent in the western part to 9 percent over the eastern portion. The albedo of the floor generally increases gradually (3 to 4 percent) along a 300- to 600-m-wide outer zone (generally depicted by unit 6) adjacent to the base of the surrounding mountains. This zone is considered to represent mixing of lighter highlands regolith with the much darker floor regolith and is remarkably narrower than the 1- to 2-km width of a similar zone at the Apollo 15 site (ref. 6-16). The lighter valley floor area between the South Massif and Family Mountain may represent a more extensive mixing zone, perhaps related to the proximity of uplands material at the surface or to its presence at very shallow depths in the subsurface. Even so, the mixing zone at the foot

FIGURE 6-64.-Orbital photomap of area shown in figure 6-63. Sun angle is 55°. Base map prepared for NASA by U.S. Army Topographic Command under the direction of the Department of Defense, 1972.

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APOLLO 17 PRELIMINARY SCIENCE REPORT implies addition of material darker than local regolith, but a ratio of 0.29 is strong evidence for the addition of dark material from another source. The increased darkening, to the south and east, of regolith developed on different geologic materials (i.e., the eastern valley floor, the Sculptured Hills, and the East Massif) is best interpreted as the effect of addition of material darker than 9-percent normal albedo from sources to the east or southeast of the Taurus-Littrow valley. The absence of any apparent ballistic shadowing by the mountains indicates that the material was transported along high-angle trajectortes. The only lunar material known to have such low albedo is dark to black glass or glassy material. A pyroclastic-like mantle of dark glassy material fits the observed geological relationships and albedo data. GEOLOGIC HISTORY

contained rock fragments for mare surfaces ranges from 0.62 to 0.68 and for highland surfaces from 0.55 to 0.68. Thus, the percentage of regolith darkening with maturity is only slightly greater for the highlands (32 to 45 percent) than for the mare (32 to 38 percent). On the floor of the Taurus-Littrow valley within the landing area, average normal albedos of the floor and the subfloor basalt blocks are 12 and 18 percent, respectively, yielding a ratio of 0.66, which is average for mare regolith darkening. In the vicinity of MOCR Crater at the eastern end of the valley, albedos of the dark floor material and the crater wall are 9 and 18 percent, respectively, giving a ratio of 0.50, which is the greatest degree of mare regolith darkening ever measured on the Moon. It is probable that some darker material (black glass?) has been deposited over and mixed with an original bedrock-derived regolith. The surface in this area, which coincides with the darkest albedo unit (fig. 6-63, unit 8), also appears somewhat smooth and subdued, in contrast to the landing area. The North and South Massifs show average albedos of _ 26 percent for fine-grained regolith and 34 percent for rocks, producing a ratio of 0.76 for regolith darkening, slightly less darkening than at Hadley Delta (Apollo 15 site). The Sculptured Hills and the East Massif show local maximum albedos that are similar to the maximums for the North and South Massifs. This similarity suggests that bedrock with similar albedo occurs in all four mountain masses, The average albedo of the Sculptured Hills and the East Massif is _, 18 percent, which gives an average regolith darkening ratio of 0.53. This is considerably darker than the 0.74 on Hadley Delta and the 0.76 on the North and South Massifs. Careful study of the Sculptured Hills and the East Massif revealed 11 small closed depressions with areas of smooth floors. The normal albedo of the regolith on the depression floors should show the maximum darkening effects because mass-wasting processes tend to expose fresher brighter material on slopes. The albedos of the depression floors decrease eastward in the northern part of the Sculptured Hills, ranging from 17 to 12 percent. The albedos of depression floors in the East Massif decrease southward beyond the mapped area from 14 to 10 percent. The regolith darkening ratio decreases from 0.50 to 0.29, which is much lower than any other measured area on the Moon. A darkening ratio of 0.50 or less strongly

Before the Serenitatis basin was formed, older major basin impacts should have covered the TaurusLittrow area with sheets of ejecta derived from still older ejeeta deposits and ultimately frmn igneous lunar crustal material. Because of their proximity, Tranquillitatis and Fecunditatis should have contributed large amounts of ejecta that may be exposed in the massifs. The older major basin impacts should also have developed radial and concentric fracture zones comparable to those around the younger, better preserved basins. Some of these fractures were presumably reactivated in the Serenitatis event. The major physiographic units (e.g., the Massifs, the Sculptured Hills, and the Taurus-Littrow valley) of this region were produced by the impact that formed the Serenitatis basin. Major radial faults bound the Taurus-Littrow valley and Mons Argaeus; major concentric faults bound the South Massif and the East Massif. Deposits of Serenitatis ejecta must have been thick and widespread. By analogy with deposits around younger multi-ringed basins such as Imbrium and Orientale, they are interpreted to comprise most of the Sculptured Hills terrain. Whether Serenitatis ejecta comprises a major portion of the massifs as well or occurs only as a veneer overlying older ejecta deposits is unknown. Deposits from the younger multi-ringed basins are probably also present but have not been specifically identified. Such deposits, which may be present on the highlands and beneath or intercalated with tire lower part of the subfloor

PRELIMINARY

GEOLOGIC

INVESTIGATION

OF THE LANDING

SITE

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basalts, could have been derived from the Nectaris, Humorum, Crisium, Imbrium, and Orientale basins, listed from oldest to youngest (ref. 6-18). Uplift of the massifs following the Serenitatis impact was probably rapid and occurred along highangle faults. Thus, the graben walls are thought to have stood at angles steeper than the angle of repose. Rapid reduction of slope angles by accumulation of thick talus wedges on the lower slopes and of mass movement deposits on the graben floor must have occurred, With the major physiographic features now formed, the next major event was flooding of the valley by lavas that filled it with _ 1200 m of basalt (sec. 10). Samples collected from the upper 130 m of the subfloor basalt show it to be similar to Apollo 11 mare basalt but slightly older with an age of _3.8 billion years. Either as a late stage of the subfloor basalt volcanism or as totally separate slightly younger events, spherical orange and black glass particles were deposited in the area of Shorty Crater and probably over much of the Taurus-Littrow region. Whether of volcanic or impact origin, the glass spheres, which solidified _ 3.7 billion years ago, were rapidly buried SO as to be preserved for eventual excavation at Shorty Crater. After subfloor basalt extrusion was completed, warping around the Serenitatis margin produced a broad anticlinal arch with the Taurus-LJttrow valley and Littrow Crater on its eastern limb. Long narrow grabens such as Rima Littrow I formed along the Serenitatis basin side of the crest of the arch, which was eventually overlapped by younger mare basalts of the Serenitatis basin. A long period ofregolith formation and accumulation of surficial deposits ensued. Some of the earlier formed regolith may be materials of Van Serg, in clasts presumably derived common. Relatively late regolith sequence are the represented by the floor which light-colored lithic from the uplands are events recorded in the formation of older, large

fling deposit was deposited on both the plains and upland surfaces during this long period of regolith formation. The unusual concentration of glass spheres in dark soils from the valley (see. 7) may represen?_ the dark mantle thoroughly intermixed with more normal impact-generated regolith. Relatively young deformational events that took place during the long period of regolith lbrmation include a slight eastward tilting of the Serenitatis basin (ref. 6-19) and the development of wrinkle ridges in Mare Serenitatis and the Lee-Lincoln Scarp in the landing area. Very recent deformation is suggested by the occurrence of small grabens on the surface of the light mantle and by the apparent youth of parts of the Lee-Lincoln Scarp. The youngest large events of special significance to the mission were the impacts that formed Shorty and Van Serg Craters in that order. Both craters are younger than the light mantle, and both penetrate deeply into the regolith.

craters (Camelot, Henry, Shakespeare, and Cochise), formation of the younger central cluster (Steno, Emory, Sherlock, Powell, etc.), and emplacement of the light mantle as an avalanche of debris that may have been triggered when ejecta struck the South Massif. Photogeologic evidence in the general TaurusLittrow area indicates that an unusually dark man-

Apollo 17 rock samples at the time of their collection (table 6-V) are shown in this appendix (figs. 6-65 to 6-87). These orientations were determined by correlating lunar photographs of samples before collection with shapes and shadow characteristics of the same samples in the LRL under oblique illumination with nearly collimated light. The light source in the laboratory simulates the Sun. It is important to emphasize that the orientations shown are those at the time of collection and do not necessarily apply to the entire history of the exposure of a rock on the lunar surface. Tumbling and turning of some rock fragments on the lunar surface has already been well documented, The small lettered cube included in each laboratory orientation photograph is not meant to indicate

lunar perspective orientations to documentary views of the same samples in orthogonal and stereoscopic photographs (mug shots) taken in the LRL using the same orientation cube. Not all tire photographs showing sample orientations are in this appendix; some have been included with the discussions of the South Massif, the North Massif, and the Sculptured Hills. Table 6-V identifies the appropriate illustrations for these samples. During the sample orientation studies, it became apparent that the special lighting used for orienting rock samples was also useful for enhancing structural and textural alinements that, for some samples, could be correlated with mappable lineations in boulders from which the samples were broken. This is especially true for the breccias. Most of the lineations in breccia samples appear to be closely spaced, thin shears. Some of these have deformed preexisting minerals and clasts or controlled recrystailization so

FIGURE 6-81.-Sample 75075, picked from the top of a large boulder, showing approximate lunar orientation reconstructed in the LRL compared to part of photograph AS17-145-22154, looking south (inset photograph, S-73-17800).

FIGURE 6-90.-Sample 72275 collected from the top of a foliated, stratified breccia boulder as shown in figure 6-8 at station 2. Compositional layering seen in the sample is apparently parallel to a set of lineaments in the boulder (S-73-17988).

The returned samples from the five previous Apollo and the two previous Luna missions include basaltic rocks and soils from four mare basins, glassy to crystalline breccias and soils from the Fra Mauro Formation and the Apennine Front, and highly aluminous, crystalline breccias and soils from two lunar highland sites. Isotopic dating of mare basalts (refs. 7-1 and 7-2) indicates that mare volcanism covered a timespan of 600 million years, beginning approximately 3.7 billion years ago. Similar studies of breccias (refs. 7-3 and 7-4)indicate anintense period of crystallization and an inferred formation of less than 200 million years, beginning approximately 4.0 billion years ago. Some anorthosltic brec_'ias from the 2- to 4-ram fragments of Apollo 16 soils have somewhat older crystallization ages of approximately 4.1 to 4.2 billion years (ref. 7:5) and may be remnants of earlier periods of formation. The breecias have undergone many generations of crushing, partial melting, and recrystallization, which has changed the initial textures of rocks from the early lunar crust. These data raise important questions concerning both lunar and solar-system history. Do the measured basalt ages represent a restricted period of lunar volcanism, or is there evidence of younger or older volcanism in the unsampled areas? Answers to such questions are crucial to understanding the lunar thermal history and the origin of lunar magmas. Do the ages of breccia formation represent a restricted period of the major impacts that shaped the lunar surface, or have only the breccias associated with the last few major impacts been sampled? Answers to these questions are of profound importance to studies of the particle flux and the accretionary history of the early solar system. Are the breccias too highly modified to identify initial textures of the early

aThe team composition is listed in "Acknowledgments" at the end of this section, 7-1

crustal rocks from which they were formed? To determine whether the early crust consisted of volcanic material, layered gabbroic complexes, or other possible rock types, the textural relationships among remnants of these materials must be studied. For the final Apollo mission, it was imperative that a site be chosen to potentially provide answers to as many of these (and other) questions as possible. From orbit on the Apollo 15 mission, the command module pilot reported seeing dark patches that resembled young cinder cones southeast of the Serenitatis basin in the Taurus-Littrow region (ref. 7-6). Steep-walled valleys with over 2000 m of relief were also evident in this area. The possibility of relatively young volcanic activity and mountains consisting of a sequence of old, large-scale ejecta blankets made this an attractive site for further exploration. Analysis of high-resolution photographs obtained during the Apollo 15 mission showed that a 6- to 10-km-wide valley between the second and third rings of the Serenitatis basin allowed access to two steep-sided mountains and a dark-mantled valley floor that might produce evidence of young volcanism (refs. 7-7 and 7-8). Detailed mapping provided five major photogeologic units for sampling: dark mantling material, a valley-filling rock unit below the mantle, a light-gray mantle apparently deposited by a slide or avalanche that spread across part of the valley floor, a group of domical, closely spaced hills ranging from 1 to 5 km in diameter (Sculptured Hills), and two steep mountains (North and South Massifs)with slopes showing several boulder tracks that were traceable from possible outcrops to the base of the slopes where some of the boulders lay within sampiing range. These boulder tracks originated at various elevations on the massifs and may represent rock types from several different units in what might be a sequence of ejecta blankets from several major impacts.

7-2

APOLLO 17 PRELIMINARY SCIENCE REPORT 2. Dark matrix breccias 3. Glass-bonded agglutinates 4. Vesicular green-gray breccias (called anorthositic gabbros by the Apollo 17 crew during the lunar traverses) 5. Blue-gray breccias 6. Layered, foliated, light-gray breccias 7. Brecciated gabbroic rocks 8. Miscellaneous: crushed dunite and black finegrained material from a dike. Basalts The basalts are generally vesicular to vuggy (fig. 7-1) and similar in both composition and texture to the Apollo 11 type B basalts (ref. 7-9), except for some of the detailed relationships between opaque minerals and pyroxene zonation. Modal estimates indicate 45 to 55 percent clinopyroxene (both pigeonite and augite), 25 to 30 percent plagioclase, 15 to 25 percent opaque minerals, and small amounts of olivine. In some instances, the olivine occurs as cores of pyroxene; but it usually occurs as phenocrysts, which generally comprise only a few percent of a rock but occasionally as much as 20 percent. Grain sizes range from coarse (1 to 2 ram) through fine to vitrophyric. In some coarse-grained rocks, the clinopyroxene may occur both as coarse, sectorially zoned phenocrysts and as finer grains in poikilitic plagioclase (fig. 7-2). There also may be fine fibrous or plumose intergrowths of plagioclase and clinopyroxene. Traces of cristobalite, tridymite, a needleshaped phase, and very fine (perhaps partly glassy) material occur interstitially to the larger grains. The vitrophyres (now largely divitrified) contain skeletal crystals of olivine (fig. 7-3) that, in some instances, display overgrowths of clinopyroxene, skeletal ilmenite and armalcolite, and a few patches of plumose h_tergrowths of plagioclase and pyroxene. For a given sampling area, the entire range of textures may be present. Opaque minerals in the subfloor basalts are present in abundances of as much as approximately 25 percent (by volume); most rocks average approximately 20 percent. Ilmenite, armalcolite, chromespinel, ulvo'spinel, rutile, metallic iron-nickel (Fe-Ni), and troilite have been identified optically; all of these minerals occur in most of the rocks. Ilmenite is by far the most abundant oxide mineral (approximately 15 to 20 volume percent); reflection pleochroism and

The lunar module (LM) landed within 200 m of the targeted landing point (lat. 20009'55 '' N, long. 30°45'57 '' E), and three traverses were completed (sec. 6). Three hundred thirty-five rocks (fragments greater than 1 cm across), 73 soils, eight drive tubes, and the deep drill string were collected. A complete list of Apollo 17 rocks and their designated types is presented in table 7-I. Several samples from large boulders were collected at stations 2, 6, and 7. From studies of samples, it is clear that the valley fill and the "dark mantle" are mare-type basalts or softs derived from them and the two massifs and the light mantle are various types of breccias and their derivatives, respectively. At present, it is not clear whether a specific set of rocks can be associated with the Sculptured Hills. In this paper, the chemical and petrographic characteristics of a representative suite of the Apollo 17 rock and soil specimens are summarized, PETROGRAPHIC GIlA RACTE R ISTICS Rocks Visual and microscopic examinations of rocks from the Apollo 17 site indicate that they are the most variable collection returned by any mission. Some rocks show the cataclastic, highly crushed textures that were common in those returned during the Apollo 16 mission. Many are crystalline breccias with petrographic characteristics that indicate varying degrees of recrystallization or partial melting. Others are friable and dark gray like the many regolith breccias of previous missions. Others display features typical of the lavas returned from the Apollo 11, 12, and 15 mare sites, whereas few have the coarse-grained igneous textures typically developed during slow crystallization from basaltic melts. Such variety is a striking contrast to the rather restricted set of complex breccias returned from the Apollo 16 highland site. In the preliminary examination, all rock samples were cleaned with a jet of nitrogen gas to remove dust coatings from their surfaces. The surfaces were then examined and described with a low-power binocular microscope. In addition, thin sections from 35 rocks were prepared and studied by conventional petrographic methods. From these examinations, the rocks may be placed in seven broad groups and two miscellaneous types, 1. Basalts

aThis inventory includes a total of 335 samples, including 132 rake samples. bB = rock chipped from boulder. Where more than one boulder was sampled at an individual station, each boulder is identified by subscripts. S = rock in bag with soft. Most of the smaller fragments in this category resulted from sieving. RS = rock from soil collected at rake-sample area. R = rock from rake sample. R* = rock collected with scoop but treated as a rake sample. CFifteen rocks weighed more than 1 kg; 111 rocks, between 25 g and 1 kg; 52 rocks, between 10 g and 25 g;and 157 rocks, less than 10 g. rocks of intermediate grain size, blocky grains of ilmenite occur in a matrix that is rich in feathery ilmenite laths (e.g., sample 72135). Vitrophyric and fine-grained basalts are rich in prisms and lozengeshaped grains of armalcolite rimmed by a selvage of iimenite. Trace amounts of chrome-spinel and chromium-ulv6spinel occur in almost all basalts; ulv6spinel commonly shows evidence of subsotidus reduction to ilmenite and metallic Fe. Metallic Fe occurs as blebs in troilite and as discrete grains that are similar to the Fe seen in other mare basalts. The similarity of basalt composition and textural variation throughout the Apollo 17 landing site suggests a similar source for all of these rocks. On the basis of the petrographic data, it is difficult to determine whether the samples represent several separate flows or different parts of a single relatively sequence thick flow that may be at the top of a thick of flows filling the valley.

Dark color indicate that much of it is rich in magnesium (Mg). llmenite crystals in the coarser grained rocks may be blocky or may display rectangular cross sections in addition to the usual lath-shaped morphology, suggesting that ilmenite may be a pseudomorph of an earlier phase. Ilmenite, especially in the coarser grained rocks, contains abundant lamellae and irregular masses of rutile on rhombohedral planes, and lamellae of a chromium_rich spinel phase parallel to the basal plane. Some metallic Fe is associated with these phases as blebs and narrow fracture fillings. In and

Matrix

Breccias

Agglutinates

The dark mat_x breccias range from friable"soil" types to a more coherent type crossed by closely spaced fracture sets that form a delicate set of irregularly shaped plates (fig. 7-4). Clasts in the breccias are primarily basalt; but, at station 9 (Van Serg Crater), the breccias contain a variety of clasts, including basalts, several types of glasses, some breccia fragments with accretionary coats, and a variety of recrystallized feldspathic rocks presumed

to be derived from the surrounding highlands. Orange glass similar to that found at station 4 occurs in limited quantities in most breccias throughout the landing site. Matrix material is largely dark-brown glass, which imparts the dark color to these rocks. A few large samples of glass-bonded agglutinates (fig. 7-5) occur throughout the Taurus-Littrow valley, Fragments are predominantly dark matrix breccias and some basalts cemented by dark-gray glass. The crew noted that these rock types occur in glass-lined bottoms of small (as much as 3 m in diameter)

FIGURE 7-4.-Dark matrix breccia from Van Serg cratering ejecta (sample 79135). Although this material is coherent enough to maintain fractures that produce small plates and wedges, the fragments are quite friable and break from the specimen during handling. Note tile various light-gray clasts, some of which are feldspathic breccias (AS17-73-15443). craters. Although most breccias and agglutinates appear to have formed by induration of the present regolith, the breccias at Van Serg Crater are more complex and appear to reflect multibrecciation events rather than a simple induration of present day regolith.

7-8

APOLLO 17 PRELIMINARY SCIENCE REPORT

0
cm

3

FIGURE 7-5.-One of the large glass-bondedagglutinates of dark matrix breccias (sample 70019) collected from the bottom of a 3-m-diametercrater (AS17-73-15333).

Green-Gray Breccias
The green-gray breccias are very coherent and consist almost entirely of a vesicular to vuggy matrix that is rich in poikilitic orthopyroxene (fig. 7-6). The degree of both vesicularity and development of poikilitic texture varies significantly from sample to sample, and, in some cases, the vesicles or vugs are several centimeters across. Mineral clasts of olivine and plagioclase and a few lithic clasts comprise a small percentage (5 to 20 percent) of each rock. One of these breccias (sample 76055) contains two distinct textures: a poikilitic and almost nonvesicutar set of fragments in a nonpoikilitic and vesicular matrix in which the vesicles are planar and well foliated, curving around the more dense fragments as in a flow structure, The matrix of the green-gray breccias generally consists of at least 50 percent poikilitic orthopyroxene (some may be pigeonite) with numerous small laths of plagioclase both inside and outside the oikocrysts (fig. 7-7). Small olivine grains occur in the oikocrysts, but they are generally concentrated along with opaque minerals outside the oikocrysts. A few rounded to angular larger clasts, scattered throughout the rock, consist primarily of plagioclase and olivine, The oikocrysts range from well developed (as much as 2 mm long and enclosing 70 percent of the matrix) to poorly developed (as much as 0.1 mm long and enclosing 5 percent of the matrix). Lithic clasts are quite rare and are chiefly feathery to equigranular, fine grained, and plagioclase-rich, Green-gray breccia occurs as a major rock type collected from boulders and smaller rocks sampled at stations 2, 6, and 7 and as smaller fragments in the light mantle at station 3; it must be considered as a 0 cm
FIGURE 7-6.-Green-gray breccia

3
(sample 76015). Although

some cavities are smooth wailed,many have drusy linings, especially the larger ones. The dark-gray coating (patina) with numerous zap pits is typical of the exposed surfaces
of this rock type. Note the scarcity of macroscopic clasts

(AS17-73-t5013). major stratigraphic unit of the North and South Massifs. These rocks are similar in texture, mineralogy, and chemistry to the poikilitic rocks collected at the Apollo 16 site (ref. 7-10). The green-gray breccias are also chemically similar to the brown-glass matrix breccias collected at the Apennine Front (ref. 7-11). Blue-Gray Breccias

The blue-gray breccias form the most complex group of rocks. This group consists predominantly of a very coherent, slightly vesicular, blue-gray matrix containing angular to subrounded white clasts (fig. 7-8). There are some cases where the blue-gray breccias seem to exist as fragments in a tan matrix, or there may be a banded relationship between blue-gray and tan matrix breccias (fig. 7-9). These rocks have no poikilitic matrix but may contain poikilitic clasts as well as mineral clasts of plagioclase, pyroxene, and subordinate olivine. Many of these mineral grains have been shocked. A few mineral clasts have fine-grained rinds that may have been partially glassy at some stage of development. The matrix also contains traces of glass (sample 73235) or divitrified glass and displays some thin bands and oriented clasts

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EXAMINATION

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SAMPLES

7-9

0
cm

I

0 nlr0 (a)

.5

FIGURE 7-8.-One of the more vesicular varieties of bluegray breccia (sample 72435). A variety of subangular to rounded feldspathic clasts are apparent. Cavities are generally smooth walled (AS 17-73-16187).

0 (b)

.1

mm

cm

FIGURE 7-7.-Thin sections of green-gray breeclas. (a) Lighter gray areas are poikilitic orthopyroxenes that compose over 50 percent of matrix and contain numerous chadacrysts of plagioclase and some olivine. Subrounded to subangular clasts are principally olivine and plagioclase (sample 77135,7, crossed polars view) (AS17-73-19912). (b) Alinement of sraa// plagioclase laths (white) is common in some areas of green-gray breccia matrices, generally in areas between oikocrysts. Several larger blocky grains of plagioclase occur as clasts (white and black). Olivine grains also occur as larger clasts (medium gray) and as smaller grains the origin of which is less certain. Note that the small laths "wrap around" the clasts (sample 76055,I1, crossed polars view) (AS17-7319877). (fig. 7-10(a)); some bands of crushed minerats contain pink spinel that also occurs in clasts (fig. 7-10(b)). The tan material is considerably coarser than the blue-gray material and contains numerous brown mineral fragments, which, in a thin section of sample

FIGURE 7-9.-Banded blue-gray and tan breccia (sample 76255). The lighter areas (tan) seem to intrude on the darker (blue) areas. The coarser grained nature of the lighter areas can be seen clearly as can the foliated nature of the light material (AS17-72-56415). 76255, appear to be inverted pigeonites with rela-

tively coarse exsolution lamellae. The blue-gray matrix ranges from a very finegrained to a coarse-grained texture. The fine-grained matrix consists of intergrowths of pyroxene and plagioclase only a few micrometers in size in some examples, whereas the coarse-grained matrix consists of subophitic pyroxene and plagioclase where some plagioclase laths may reach 50 to 100/_m in length. In contrast to the green-gray breccias, alarge proportion of the mineral clasts are pyroxenes of various types. Lithic clasts include very-fine-grained, prob-

7-10

APOLLO 17 PRELIMINARY SCIENCE REPORT crew as being a major part of the large boulder at station 6, where it was in contact with green-gray breccia. The latter contained several inclusions of blue-gray breccias near the contact, suggesting that the green-gray breccias were largely fluid at the time of incorporation. Layered, Foliated, Light-Gray Breccias

.j

0 mrn

.5

The layered, foliated, light-gray breccias contain approximately 60 percent matrix and are less coherent than the green-gray and blue-gray breccias. There is some variability in the coherence of the light-gray breccias, apparently as a result of the degree of annealing of an originally glassy matrix, some of which remains as glass. On a macroscopic scale, these breccias are nonvesicular to very slightly vesicular. A large proportion of clasts in these breccias have white, feldspar-rich cores rimmed by a dark-gray glass-rich material. In the less coherent breccias, clasts stand out in relief on eroded surfaces. On both macroscopic and microscopic scales, there occur white veins, layers, and lenses that, in some cases, appear to intrude the light-gray matrix (fig. 7-11). The light-gray matrix consists of numerous small fragments of lithic debris, plagioclase, olivine, pyroxerie, and opaque minerals set in a brown, glassy to very fine devitrifled mesostasis. The white veins and lenses contain no brown interstitial material but consist of a few lithic fragments of the gray matrix breccias and mineral debris that is largely feldspathic. Mineral fragments are mostly plagioclase but also include olivine, pyroxene, and spinel. Lithic fragments are primarily breccias but also include anorthositic types, basalts, and poikilitic rocks. Some clasts show accretionary structures consisting of brown, glassy matrix mantles surrounding lithic cores (fig. 7-12). Breccia clasts within breccia clasts indicate a complex history for the formation of the light-gray breccias. This rock type is found as a boulder at station 2 and among the smaller fragments in the light mantle at station 3; therefore, it appears to be associated with the South Massif. B recciated Gabbroic Rocks

0 mm

.1

FIGURE 7-10.-Thin sections of blue-graybreccias.(a) Clasts and very-fine-grained dark matrix of bine-gray breccia (sample 76315,11). Note the alinement of elongate clasts and foliation of light and dark streaks in matrix. Several pink spinels (medium gray) occur in the light band atong the edge of the photograph (plane light view) (AS17-7319998). (b) Clast in blue-graybreccia (sample 76315,11). Several equant, pink spinels (medium gray) occur in this plagioclase and olivine clast, suggestinga source for the crushed material in the spinel-bearinglight band of figure 7-10(a) (plane light view)(AS17-73-20000). ably devitrified material, poikilitic rocks, relatively coarse-grained anorthositic types, feathery feldspar intergrowths, and basalts. The blue-gray breccias occur as a major part of the boulders, as smaller rocks at stations 2, 6, and 7, and as fragments in the light mantle at station 3; they must be considered a major stratigraphic unit on both massifs. The blue-gray breccia was reported by the

Several samples consist of brecciated or crushed anorthositic to gabbroic rocks. Some samples show evidence of crushing with little or no mixing, thus

PRELIMINARY

EXAMINATION

OF LUNAR

SAMPLES

7-11

l 0
Cra

I 3 (a)

L 0
mill

I .5

FIGURE 7-11.-Layered, follated, light-gray hreccia from a boulder at station 2 (sample 72215). The darker areas that appear in some instances to be clasts are very fine grained, probably devitrified. The lighter areas that appear to be veins are essentially crushed crystalline material (AS17-73-16661).

allowing

possible

reconstruction

of original

textures.

For example, a coarse norite (sample 78235) shows a good cumulate texture on a macroscopic scale (fig. 7-13), but it has undergone some crushing on a microscopic scale (fig. 7-14). Conversely, a gabbro (sample 78155) has been highly crushed and may be mixed as well (fig. 7-15). One rock (sample 76535) is a coarse-grained norite and shows no signs of having been sheared (fig. 7-16); although there', are no thin sections of this rock, it may well have maintained its original texture. In another example (sample 77017), the degree of crushing appears to vary from a margin injected with glass veins to a less disturbed inner region of cumulate plagioclase and olivine in clinopyroxene oikocrysts (fig. 7-17). Two crushed and recrystallized anorthositic rocks were sampled from large clasts in the blue-gray breccia portions of the boulders at stations 6 and 7 and may present some clues to the source region of this breccia. Some of the less crushed and mixed samples of these originally and a fine-grained black dike with a very-fine-grained igneous-looking matrix from the large boulder at station 7. The dunite contains over 95 percent olivine as millimeter-sized fragments in a crushed matrix of the same material (fig. 7-18). Chemical analysis of this rock indicates an olivine in the Fo85-9o range. The black dike appears to originate within the blue-gray breccia part of the station 7 boulder and _ ram (b) FIGURE 7-12.-Thin sections of light-gray breccias. (a) Glassy to devitrified rounded clasts (black) in a matrix of more crystalline debris. However, the matrix at top of photograph is more glass-rich and similar to elasts (sample 72275,11, plane light view) (AS17-73-20085). (b) Crystal clasts in a brown-glass matrix (black) that itself forms a clast in a matrix of glass and crystalline debris (sample 72255,7). In some cases, these brown-glass matrix clasts contain breccia clasts in addition to mineral fragments (plane light view) (AS17-73-20082). ._

coarse-grained rocks may present the be:st opportunities from all of the Apollo missions for reconstructing the textures and mineral compositions of rocks from the early lunar crust, Miscellaneous Rocks

The miscellaneous rocks include a dunite sample from a large clast in one of the boulders at station 2

7-12

APOLLO

17 PRELIMINARY

SCIENCE

REPORT

FIGURE

7-15.-Thin

section

of

crushed

and

stirred

anortho-

cm

3

FIGURE 7-13.-Coarse-grained norite (sample 78236) with glassy-appearing plagloclase and crushed pyroxene. Note the dark glassy coating on the lower right side of rock. This glass occurs also as veins in the rock (AS17-7315393).

SOl IS Soils were collected by the Apollo 17 crew to aid in characterizing four major photogeologic units determined by preflight studies: (1) the "dark mantie" that covers the plains surface and was interpreted as a possible pyroclastic deposit overlying basalt flows, (2) the South Massif and the light mantle that was interpreted as an avalanche deposit from that massif, (3) the North Massif that was interpreted as highland breccias or possibly volcanic domes, and (4) the Sculptured Hills that were interpreted as highlands terrain composed of breccias. Five core tubes, one 2.92-m-long drill core, and 73 soils, including both surface samples and samples from several trenches, were collected. All soils were

FIGURE 7-14.-Thin

._ tara section of coarse-grained norite (sample

described surficially in the Lunar Receiving Laboratory; 64 were sieved into five size fractions, and 18 were studied further in thin section and by additional sieving.

78236), showing area of crushed plagioclase and pyroxene (top half of figure), large plagioclase crystals that are largely isoixopic (white), and a brown-glass vein (lower right) (plane light view) (AS17-73-19929). crosscuts an anorthositic norite clast. Although the dike contains approximately 15 percent mineral clasts, the remainder of the dike consists of 5- by 10-/zm plagioclase laths in 30- by 50-gm pyroxene oikocrysts. Within 0.5 mm of the contact, the vein material decreases in grain size, and the plagioclase becomes more skeletal in form.

Grain-Size Analyses
The methods of grain-size analysis are outlined in McKay et al. (ref. 7-12). The mean grain size of soils from the black-mantled terrain ranges from near the mean grain size for lunar soils (_ 70 ;tm) to 125 gm (table 7-1I). The softs from the North and South Massifs are fine grained (coarse silt size), with mean grain sizes of 45 to 64 /lm. As in most lunar soils, nearly all these soils are very poorly sorted. Soils

PRELIMINAPY

EXAMINATION

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7-13

cm

_

0

nl[n

.5

FIGURE 7-16.-Coarse-grained norite (sample 76535) with fresh-appearing plagioclase (white to light gray) that has typical striations of albite twinning. Although pyroxenes (medium gray) are fractured along cleavage planes, they do not appear badly crushed (AS17-73-19458).

FIGURE 7-17.-In an anorthositic rock having a generally crushed texture, this area shows several blocky to lath-shaped plagioclase grains (white) in optically continuous augite (gray) that extends over most of the photograph, except the upper left corner. A few very thin glass veins (black lines) occur (sample 77017,11, plane light view) (AS 17-73-20008).

from

station

4 composed

predominantly

of glass

spheres have median are poorly sorted.

grain sizes of 40 to 43 btm and

Soils from Soils from stations

the "Dark 1 and

Mantle"

5 and the LM area are

mostly the comminuted products of basalt. The bulk of these soils is composed of basalt fragments, agglutinates, and grains of clinopyroxene, plagioclase, and ilmenite (table 7-III). The basalt fragments have a range of texture and composition, although two types are most common. 1. Equigranular to subophitic, medium to coarse crystalline basalt containing 50 percent cllnopyroxene (augite and pigeonite), 25 percent feldspar, and 25 percent ilnrenite. Olivine, cristobalite, and opaque phases are present in lesser amounts. 2. Finely crystalline, variolitic basalt with titanium augite, ilmenite, and plagioclase, Agglutinates, a ubiquitous component of lunar soils (refs. 7-12 and 7-13), consist of mineral and lithic detritus bonded by grape-like clusters of nearly opaque, brown glass. In soils from the plains floor, the agglutinates have a dull, nearly metallic luster in contrast to agglutinates in soils from the massifs, Coarse-grained agglutinates (250 to 500/lm) are very vesicular and contain irregular, coalescing cavities 5 to 150/amlong.

.5 mm FIGURE 7-18.-Thin section of dunite with large olivine crystals set in a crushed matrix of the same material comprise this entire clast (sample 72415,12, plane light view) (AS17-73-199471.

0

In the

< 1-mm fraction,

there

is a considerable

difference between the surface and the trench-bottom (-17 cm) samples at station 9. The surface sample contains twice as much agglutinate as the trench-bottom sample and very different breccia components (table 7-III). The finer fractions may be mostly comminution products of the dark-gray vitric brec-

7-14 cias that are the most common 9.

APOLLO

17 PRELIMINARY at station

SCIENCE REPO R T boundaries between the two gray softs. A core driven

rock types

Station 4 is on the rim of Shorty Crater, which appears to be a crater that penetrated the thin white mantle and ejected mostly dark plains material. At station 4, three of the most unique soils from the Apollo 17 site were collected: orange, gray, and black. The orange soil forms a band with sharp TABLE 7-11.-Grain-Size

through the band penetrated a black soil. Thus, the three soil types are present within a few square meters. The orange soil (sample 74220) consists of cohesire clods that withstood transport back to Earth. At least one of these clods has color zoning, having a pale orange-brown center and a moderate orangeof Some Apollo Inclusive standard graphic deviation 2.08 2.02 3.30 3.32 2.62 2A2 2.58 2,02 2.94 2.94 1.70 1.59 2.03 1 7 Soils

PRELIMINARY EXAMINATION OF LUNAR SAMPLES brown rim. Contacts between the zones are sharp, Surficially, the soil is composed of ruby-red to black glass spheres and broken spheres that, in thin section, are homogeneous, pale orange, and nonvesicular. There is no evidence of included detritus in the orange glass, but there is a trace of olivine phenocrysts. Nearly half the orange glass spheres are partly or completely crystallized to small sheaf-like bundles of very fine crystals to parallel bars of ilmenite and olivine, Black soil from the bottom of the core at station 4 (sample 74001) consists mostly of barred or broken spheres. These spheres may be completely crystallized equivalents of the orange glass droplets, consisting of olivine and orthopyroxene (?) phenocrysts in a very small amount of brown to orange glass. These spheres are crossed by ragged, thin ilmenite plates that impart the black color to this soil. Traces of spinel and metal are present. The core soil also contains 10 to 20 percent completely devitrified brown-glass spheres that are purple in thin section, The gray soils (samples 74240 and 74260) that flank the band of orange soil contain a variety of components (table 7-III), including a significant amount of "ropy" glass that occurs as light-gray spindle-shaped droplets with abundant, fine-grained,

7-15

angular detritus welded to the grain surfaces. The various orange and black soil components are present in nearly all of the "dark mantle" soils in portions of 5 to 20 percent of the total mass of the sample ,(average is 10 percent). These components are also present in low-grade breccias from the plains. A surface sample at the LM area (sample 70180) contains approximately 8.1 percent (by weight) of these "'exotic" components (table 7-IV). As illustrated in table 7-IV, most of the exotic components are in the < 100-/_m fraction and are not adequately :represented in table 7-III. The wide distribution of these glasses beyond the limits of Shorty Crater is a possible indication that layers of this material are present to depths of tens of meters below the present valley floor and axe penetrated by the deeper impact craters. The mfiformity of composition and morpho[ogy of the "exotic" components supports a theory that these components are droplets formed during lava fountaining, which would form lenses or layers within the strata underlying the Apollo 17 landing site. It is possible that the components were subsequently buried by lava flows; they have no agglutihates and appear to have had no history of exposure at the lunar surface before their exhuming as ejecta at Shorty Crater.

APOLLO 17 PRELIMINARY SCIENCE REPORT observation agrees well with the interpretation of the light mantle as an avalanche deposit from the South Massif. North Massif The coarse fraction of soils from stations 6 and 7 consists of mostly patchy, medium-gray to dark-gray breccias, with lesser amounts of white breccias and agglutinates. The < 1-mm fraction is characterized
abundant plagioclase and pyroxene grains, low-grade

brown-glass breccias, and medium-grade breccias (table 7-III). Some of the medium-grade breccias have a poorly defined poikilitic texture. North Massif soils have more breccias of medium metamorphic grade and a higher plagioclase content than South Massif soils. However, they are not greatly different from South Massif soils.

aStation 10. bTotal percent = 8.13. South Massif and Light Mantle

The South Massif and the light mantle or avalanche deposits were sampled at stations 2, 2A, and 3; these appear to be the comminution products of a variety of breccias with a trace of mare basalt (table 7-III). Viewed superficially, the coarser fractions consist of mostly medium-gray fine-grained breccia. Dark-gray breccias with white clasts < 1 mm in diameter were evident in lesser amounts, Vitric breccias of low metamorphic grade, 1 to 3 of Warner (ref. 7-14), contain 1- to 200-#m-long clasts of mineral and lithic detritus in matrices of brown, colorless, and banded glass. Most of the clasts consist of angular feldspar grains with lesser amounts of clinopyroxene or orthopyroxene; however, some grains contain a myriad of clast types, Breccias of medium metamorphic grade, 4 to 6 of Warner (ref, 7-14), have fine-grained to coarse-grained equigranular textures; they are composed of mostly feldspar and orthopyroxene, with traces of ilmenite and olivine. White and gray marbled units from the trench at station 3 have nearly the same mineralogic composition, but the gray layer has a higher agglutinate content. Similar white and gray units exist in a mottled texture at station 2A. Assuming that the gray, agglutinate-rich units represent surface layers, it is possible that a layered regolith sequence was mixed as it avalanched down the slopes of the South Massif. Soils from the South Massif and the light mantle contain the lowest content of mare basalt and the largest variety of breccias of any Apollo 17 soil; this

Sculptured Hills At station 8, a surface soil and a soil from the bottom of a 25-cm-deep trench differ mainly in their relative maturity; the trench soil contains twice the amount of agglutinates. Breccia types in soils from the Sculptured Hills are nearly the same as those in soils from the South Massif (table 7-Ili); but there is a greater amount of basalt in both the Sculptured Hills soil samples as compared to those from the South Massif. At station 9, located between the Sculptured Hills and the LM, the soil composition in the "dark mantle" appears to be transitional between the two stratigraphic units. The coarse-grained fraction of station 9 soils consists of dark-gray, fine-grained, vitric breccia fragments and aphanitic basalt. C H EM ICA L C HA RACT E R ISTI CS Rocks Nearly all chemical characteristics of the Apollo 17 rocks can also be found in rocks from previous missions. Mare basalts with high iron oxide (FeO) and titania (TiO2) contents, noritic breccias with a major element composition broadly similar to KREEP (potassium, rare-Earth elements, and phosphorus; here called KREEP-like rocks) but with roughly one-half the minor and trace element content, and brecciated anorthositic gabbros with relatively high lime (CaO) and alumina (A1203) contents have all

PRELIMINARY

EXAMINATION OF LUNAR SAMPLES

7-17

been observed previously. However, unusually high zinc (Zn) concentrations in the orange soil and the exceptionally low Ni content of the basalts suggest different source materials than those for previously returned igneous rocks. The trace element contents of the anorthositic rocks are significantly different from nearly all those previously returned, again suggesting variations in the source regions. Basalts Basalts exhibiting wide textural variation have been extensively sampled in the vicinity of Steno and Camelot Craters (stations 1 and 5), the LM and Apollo lunar surface experiments package (ALSEP) site, and also from Shorty Crater (station 4). Analyses of three of these samples are given in table 7-V. The basalts are characterized by high FeO contents and by correspondingly high FeO/MgO (magnesia) ratios (fig. 7-19); hence, they are similar to other mare basalts sampled at the Apollo 11, 12, and 15 and the Luna 16 landing sites. These characteristics and low soda (N%O) concentrations distinguish mare basalts from all terrestrial basalts, In detail, these basalts have high TiO_ and correspondingly low silica (SiO2) concentrations and are broadly comparable with basalts from Mare Tranquillitatis (figs. 7-20, 7-21, and 7-22). The sulfur (S) content of these rocks, about twice that found in the Apollo 12 and 15 basalts, also compares closely with the Apollo 11 basalts. The Ni content (approximately 2 ppm), exceptionally low even for lunar rocks, is much lower than in previously sampled mare basalts. One sample (75055) is slightly quartz normative and compares closely in both major and trace element chemistry with typical low potassium (K)Apollo 11 basalts. The other two analyzed basalts (samples 70035 and 70215) differ from sample 75055 in that they are olivine normative and higher in TiO2 (fig. 7-20) and MgO than low-K Apollo 11 basalts, and are correspondingly lower in SiO2, A1203, CaO, and the trace elements rubidium (Rb), zirconium (Zr), yttrium (Y), and strontium (Sr). Although chemically comparable, these two basalts differ in texture, Sample 70215 is very f'me grained (probably a devitrified vitrophyre), whereas sample 70035 is a coarse-grained (1 to 2 mm) vesicular basalt. The aphyric texture of sample 70215 indicates that high-titanium magmas have been erupted onto the

lunar surface and that rocks of this composition are not necessarily of cumulate origin. The compositional differences observed between sample 75055 and the other two samples are too large to have been produced by near-surface crystal fractionation, indicaring that at least two basalt types have been sampled at the Apollo 17 site. Massif Rocks Rocks from the South and North Massifs have been sampled at stations 2, 3, 6, 7, and 8. Analyses of representative samples are given in table 7-V. In contrast to the wide textural and petrographic variations observed in these rocks, two distinct, chemically defined rock types can be recognized: noritic breccias, corresponding to the petrograpMcally defined suites of green-gray, blue-gray, and light-gray breccias; and anorthositic gabbros, corresponding to the petro. graphically defined suite of brecciated gabbroic rocks. The latter group was found as clasts in the noritic breccias and as isolated samples at stations 6, 7, and 8. Figures 7-21 and 7-22 show that both rock types plot close to the plagioclase-control trend that is typical of highland rocks, particularly those from the Apollo 16 site. The Apollo 17 noritic breccias are characterized by approximately 50 percent normative plagioclase and are broadly comparable in bulk chemistry with KREEP-like rocks sampled on previous missions (e.g., samples 15265, 62235, and 60315). The noritic breccias have slightly higher A1203 concentrations and MgO/FeO ratios than typical Apollo 14 breccias (fig. 7-21); in this respect, they are more closely comparable with the Apollo 16 KREEP-like rocks (figs. 7-21 and 7-22). Although closely comparable in major element chemistry, the noritic breccias are lower in Na2 O, potash (I(2 O), and phosphorus pentoxide (P2Os) than the Apollo 14 breccias, but they resemble the broadly defined composition of low- to moderate-K Fra Mauro basalt composition proposed by Reid et al. (ref. 7-15) on the basis of glass compositions in the Apollo 15 soils. Elements that are abundant in KREEP, such as Rb, Y, Zr, and niobium (Nb), are also lower in these rocks than in the Apollo 14 breccias. Figure 7-23 shows that, in comparison with their abundances in Apollo 14 breccias, these dements are depleted in rocks with the major element composition of KREEP from the Apollo 17, 16, and 15 sites. In all cases, K and Rb are

more depleted than sodium (Na), phosphorus (P), Y, Zr, and Nb, but Sr is only slightly depleted. The Apollo 17 noritic breccias and the brown matrix breccias from the Apollo 15 site are more depleted in these elements than the KREEP-like rocks from the Apollo 16 site. Some internal variation within the Apollo 17 noritic breccias is illustrated in figure 7-23. Sample 72275, classified petrographically as a follated, lightgray breccia, is characterized by lower Sr and Na and higher P, Y, and Zr concentrations tha:a the other breccias. These differences in minor and trace elemerit abundances accompany small but important differences in major element chemistry. These differences include higher FeO and CaP in sample 72275 for a given AI_O3 content and distinctly lower MgO/FeO ratios, reflected in a higher normative

orthopyroxene content relative to plagioclase and olivine. These differences indicate that the foliated, light-gray breccias are derived from a different lith()logical than the other gray matrix breccias. This unit distinction is emphasized by the much lower Ni content of this rock compared with the other noritic breccias (table 7-V). If the Ni content is largely of meteoritic origin, then the possibility exists that the foliated, light-gray breccias form a stratigraphic unit the materials of which have undergone a much

samples of anorthositic gabbro have been (table 7-V). The samples are of restricted

.8 .6

composition, plagioclase. all containing normative They just over 70 percentin compare broadly major element chemistry with such samples as 15418 and 68415 and with the highland basalt composition (ref. 7-16). Figure 7-21 shows that they mafic than from more comparable rocks 16 site. The trace element contents of particularly Zr, Y, and Sr, tend to be are slightly the Apollo these rocks, lower than

those in the Apollo 16 rocks, being slightly over half their content in sample 68415 (ref. 7-9). In this respect, the samples are more closely comparable with sample 15418 (ref. 7-10 and fig. 7-24), providing evidence for a spectrum of trace element concentrations in rocks with the bulk composition of anorthositic gabbro. Soils

The compositional range of soils from the Apollo 17 landing site is greater than that found at any previous landing site. There is a complete range of soils-from those approaching the basalt in composition to the highly aluminous, light mantle soils derived from the South Massif. Analyses of 17 soils from most of the major sampling stations and an analysis of Apollo 11 sample 10084 are given in table 7-VI. The latter sample is included for comparative purposes and as an indication of the accuracy of the results. The major element chemistry of these soils appears relatively straightforward, suggesting a simple two-

In addition to the clasts of anorthositic gabbro, clasts of dunite and olivine are also present in the noritic breccias. An analysis of a large dunite clast (72415) sampled at station 2 is given in table 7-V. Abundant inclusions of olivine and dunite in sample 76055 are reflected in the high MgO content of this sample and in the low trace element abundances compared with the other breccias (fig. 7-23). Sample 76055 is slightly displaced in composition toward the dunite clast (sample 72415) from the other noritic breccias (figs. 7-21,7-22, and 7-24).

PRELIMINARY EXAMINATION OF LUNAR SAMPLES component mixing trend involving basalt and an aluminous end-member intermediate in composition between the noritic breccias and the anorthositic gabbros (figs. 7-19, 7-21, and 7-22). In detail, however, the mixing is more complex because three compositional groups can be recognized, largely on the basis of trace and minor elements (fig. 7-24). In addition to compositional distinctions, selenograptdc distinctions can be made among these three groups, "Dark Mantle" MateriaL-Soft samples taken at stations 1 and 5 are considered to be the best candidates for "dark mantle" material, particularly sample 75061, a soft sampled from the top of a boulder. The samples are of uniform chemistry and are compositionally very close to the subfloor basalts (figs. 7-19, 7-21, 7_22, and 7-24), which, together with orange-glass fragments, constitute approximately 80 percent of these soils. The remainder is accounted for by aluminous material from the adjacent massifs. Softs from station 4 and the LM-ALSEP site are slightly more aluminous and less mafic than the station 1 and 5 soils, containing slightly more of the massif component, The Ni content of these softs is fairly constant, averaging approximately 120 ppm in the station 1 and 5 softs, but it increases with the increasing aluminous component in the other softs. Because the basalts, which account for the bulk of these softs, are very low in Ni (table 7-V), most of the Ni in the soft is probably of meteoritic derivation, corresponding roughly with a 1-percent chondrite component. Light Mantle Material.-Light mantle, derived from the South Massif, has been sampled at stations 2, 2A, and 3. These softs are the most aluminous sampled at this landing site, and, apart from a small (5 percent) basaltic component, they are intermediate in both major and trace element chemistry between the noritic breccias and anorthositic gabbros (figs. 7-19, 7-2.1, 7-22, and 7-24). If the light mantle is representatixle of the South Massif, it implies that the massif is composed predominantly of noritic breccias and anorthositic gabbros in roughly equal proportions, The average Ni content of these softs is approximately 220 ppm. If one allows for the high Ni in the source rocks (approximately 100 to 120 ppm)_ which may also be of meteoritic origin (during an earlier phase of lunar history), then the meteoritic component inferred for these softs is approximately 1 percent, similar to that previously inferred for "dark mantle" softs, North Massif and Sculptured Hills MateriaL-Softs

7-21

collected near the North Massif and the Sculptured ttills from stations 6, 8, and 9 are more aluminous zLndless mafic than the "dark mantle" and related toils from the valley floor, and they are intermediate in major element chemistry between the bas_ilts and the light mantle softs (figs. 7-19, 7-21, and 7-22). Itowever, these soils are depleted in K, Zr, and Y with _espect to a simple mixture of these two end components. This fact is illustrated in the case of Zr in figure 7-24. Thus, in these softs, anorthositic lgabbro is more abundant relative to noritic breccias than it is in the light mantle softs, suggesting that anorthositic gabbro may be more abundant in tile North Massif or the Sculptured Hills (or both) than it is in the South Massif. Orange Soil

The orange soil (sample 74220) sampled at Shorty Crater is composed almost entirely of glass and devitrified glass spherules. It differs markedly in composition from all other softs, including adjacent softs from station 4 (table 7-VI), and is broadly comparable with the basalts, having high FeO and 'FiO2 concentrations. In contrast to these rocks, the orange soil contains 14.4 percent MgO and could be ,derived from the basalt composition by the addition of approximately 24 percent olivine (Fo66). However, both the Sr and Rb abundances (table 7-VI) are too high in the orange soil with respect to the basalts, thus precluding a direct relationship between the two. The Zn content of 292 ppm is exceptionally high for i[unar materials (table 7-VI); the only other material ;approaching this composition is the Apollo 15 green i_ass (60 to 100 ppm) (ref. 7-18). The high volatile element content of the orange soft (in addition to Zn ;and abundant chlorine (CI), found semiquantitatively ,during preliminary examination and confirmed by G. W. Reed (personal communication)) implies a source .different from that of the basatts, irrespective of whether the glass in the soft is of volcanic or impact origin. Furthermore, the high Zn content cannot be attributed to any reasonable level of meteoritic contamination during impact. Because Zn concentrations in both the basaltic and massif rocks are low, approximately 2 to 5 ppm, the higher concentrations observed in the softs (table 7-VI) must reflect the orange-glass (or its devitrified derivatives) content of these softs. On this basis, the orange-glass content is highest in the other softs from

those found during earlier missions. The majority of the samples depicted in figure 7-25 have values ranging from 110 to 170 ppm C, which is typical of mature dark-colored soils. Exceptions include the orange soil (sample 74220), its adjacent soils (samples 74240 and 74260), and samples 71041, 71501, and 71061 from station 1. The analyzed split of sample 71061 has a noticeably larger grain size than normal f'mes,

Because C abundance has been shown to be correlated with surface exposure and the proportion of finer material, it is not unexpected that the coarser :fines would be lower in C. The results verify previous !proposals that the major portion of C found in lunar :fines is from solar wind. Although the value recorded :for the orange soil (sample 74220) is 4 ppm C, an earlier split was analyzed and had t00 ppm C. The 4 ppm C from a carefully selected and handled sample

7-24 8501 300- 0181 0161

APOLLO 17 PRELIMINARY SCIENCE REPORT A-lfi ,, / A-11 A-15 troilite, with the silicates in the matrix (ref. 7-19). A-11 The SO2 resulting from the reaction products is seen (less than 8 ppm) of CO2 (ref. 7-20) over a wide t° 1200° C' interval lunar 200 ° ev°lve trace and it has temperature Mature from s°ils to 500 ° C, am°unts been proposed in the temperature interval from 1000 ° in figure 7-26 by Hayes (ref. 7-21) to represent CO2 that has been reimplanted from the lunar atmosphere. The low abundance of solar wind hydrogen (released from 200 ° to 700 ° C) for sample 74220,5 lends support to the observation of an almost 7-22) lackthe agglutinates and a low exposure age (ref. total for of sample. Additional gases released above 700 ° C are reaction products of components found in the soil. Cosmic-Ray-Induced Radionuclides

100?0 200_ 40 -" -

5081 1041 65012501 I!_12 i!50! •4240 A-14 2701A'161 +t 4260:1061

9135 t + ' A._17 A-16

![i

A-11 $ A-12 _ A_17 8155 tA.* 1 4

A-14

,_ 10_: 7 A-17 4220 Soils

A-15

A-16 Breccias I Rocks

4 2

FIGURE 7-25.-A comparison of the total carbon abundances for the Apollo 17 samples with those of samples from previous missions.The latter data are from reference 7-9. Apollo 17 samples are shown by the last four digits of the inventory number,

The amounts of radioisotopes produced on rock surfaces and on the top few millimeters of soils from the Apollo 17 site (table 7-VII) are much larger than amounts observed in samples from previous Apollo missions. These high activities resulted from a series of solar flares that occurred from August 2 to 12, 1972, the largest solar cosmic ray event that has ever been observed on Earth (ref. 7-23). Sodium-22 (22Na) activities doubled when compared to the values seen for Apollo 11, whereas cobalt-56 (S6Co)and manganese-54 (S4Mn)activities increased an order of magnitude in some cases. The isotopes beryllium-7 (TBe), chromium-51 (SlCr), and 58Co were observed for the first time in lunar samples, and more definitive numbers for STCo content were obtained. The measurements of these additional isotopes and the increased activity of the oilier isotopes should serve as a better baseline for processes involving interaction of solar protons with the target dements involved. Several rock samples appear to be unsaturated in aluminum-26 (_6A1) (samples 70255, 78135, and 78235), but, because these samples are chips from large rocks, chemical analysis will be necessary for confirmation. D R IV E TUB ES A N D D R IL L CO R E Three double drive tubes, two single drive tubes, and a deep drill core were collected to sample the stratigraphy of stations 3, 4, 6, and 9, and the ALSEP and LM sites. On return, these samples were assigned an inventory number, unpacked, externally cleaned,

is considered valid for sample 74220; the earlier high value is attributed to contamination in some form, although real variations in the sample cannot be completely ruled out. The soil breccia (sampie 79135) has a normal total C content of 150 ppm, and the anorthositicgabbro (sample 78155) has a value of 21 ppm C, which is similar to anorthositic rocks from Apollo 15 and 16. The gas-release proffde (fig. 7-26) for the orange soil (sample 74220,5) is distinct for any lunar sample, The sample shows evidence of water (H2 O), carbon dioxide (CO2), and sulfur dioxide (SO2) loss below 350 ° to 400 ° C. The abundances, temperature release ranges, and sequence of release are different from lunar soils that have been derived through normal lunar regolith processes. The release profile for H20 is similar to the release of absorbed water (released below 150 ° C) and a more tightly bound H20 component, which might be associated with the large abundance of glass in the sample. The low-temperature release of CO2 (from 10 to 15 ppm CO2) and of SO2 (from 10 to 15 ppm SO2) is especially unusual, Mature lunar soils do not evolve SO2 until temperatures approach 800 ° to 900 ° C. The high-temperature SO2 results from the reaction of sulfides, such as

FIGURE 7-26.-Gas-release profile of soil sample 74220,5 (orange soil). Note the low-temperature release of CO= and SOz. The gas-release patterns as compared to temperature have been plotted so that each of the gases have been normalized to 100-percent amplitude in their region of greatest abundance. The arrow on the weight-loss curve represents the initial melting of the sample. (a) Gas-release profile. (b) Weight-loss curve. weighed, and then transferred to the Core Studies Laboratory. The drill stems and drive tubes were X-rayed with Fe radiation for 5 sec at 90 kV and 50 mA. Descriptions are derived and illustrations in the following section from the study of X-radiographs and the guide to stratification and dissection as well as a permanent, three-dimensional record of the location and attitude of many rock fragments. Changes in size, shape, sorting, packing, and composition affect the opacity of X-radiographs; structures and sampling also, primary depositional artifacts are readily visible.

examination of samples taken from the upper ends of some deep drill sections. The samples were described under the binocular microscope and split into coarse and fine fractions. The fine fractions were allocated to Principal Investigators; photographed and stored. the second section from the coarse fractions were The drill bit (70001) and the top of the deep drill

Because particles with a low X-ray absorption, such as feldspars, tend to be invisible, data on grain size, sorting, and density may be ambiguous. The exact location of components may be uncertain because of parallax distortion.

Deep Drill Core
The deep drill core was taken at the ALSEP site, z_pproximately one crater diameter east of the 400-m-diameter Camelot Crater. Following extraction, the drill string segments for return: was broken down into three 70001 to 70004, 70005 and

string (70008) were dissected, and the material was described under the binocular microscope. Samples were also removed from two drive tubes: from 70012 because of a spillage problem and from 74001 for scientific purposes, The stereopair X.radiographs provide a preliminary

APOLLO 17 PRELIMINARY SCIENCE REPORT The fine-grained middle interval, which is 56 cm thick, includes units 36 through 51 and contains a few widely scattered coarse rock fragments. The sample removed from the top of 70005 contains small, anorthositic rock fragments and a few breccias; X-ray characteristics indicate similar texture and composition throughout the interval. The 131.5-cm-thick basal interval, which is heterogeneous and well stratified, includes units 1 through 35. Although there are some units over 10 cm thick and others less than 0.5 cm thick, most range from 2 to 5 cm. Similarly, although sorting ranges from very poor to good and grain size ranges from medium coarse to very t'me, most soils of this interval are well sorted and free grained. Samples removed from the top of sections 70004, 70003, and 70002, and from the dissected bit, 70001, tend to be fine grained and moderately well sorted, with a small percentage of coarse fraction dominated by soil and glassy matrix breccias. Although vesicular basalts and gabbros are present, they are subordinate to glasses and breccias. Field and stratigraphic data suggest the following tentative subfloor regolith stratigraphy and history. The lower interval, with its many thin layers, relatively fine grain size, good sorting, and abundance of breccia and glass, was deposited either slowly by accretion over a long period of time or rapidly with extensive reworking over a long period of time. The middle interval, which is fine grained, relatively well sorted, and rich in powdery anorthosite, could signify either the culmination of the working and slow accretion of beds of the lower interval or the distal end of a landslide from one of the massifs. The upper interval appears to be associated with events that produced nearby craters. The lower strata (fig. 7-28) may be ejecta from subdued older craters, such as Poppy and San Luis Rey. In 70008, the reverse stratigraphic sequence of soil breccia through glassy breccia to crystalline rocks, the abundance of fresh-appearing plagloclase, and the scarcity of breccia and spatter glass are taken as evidence to indicate that the main unit accumulated by rapid deposition, probably from the Camelot cratering event. The thin, fine-grained bed above unit 59 may represent an eroded and pulverized horizon. The uppermost, fining-upward, thin-bedded sequence (units 61 through 64) is tentatively interpreted to be base surge ejecta from nearby Rudolph Crater, which does not contain coarse, blocky, subfloor ejecta. This sequence was not found in drive tube 70012, where a hard layer probably represents the packed fragmental unit.

70006, and 70007 to 70009. Each section has a potential collecting length of 39.9 cm, except for the basal section (70002), which is 37.0 cm long attached to the 6.5.cm-long bit (70001). From X-radiographs, the estimated length of returned sample was 294.5 cm (9.66 ft) out of a potential return of 322.5 cm (10.6 ft). Because drilling became difficult and was stopped with 30 + 2 cm of the drill stem still above the lunar surface, a void of similar length at the top of the core was expected. Actual empty space occupied approximately 27 cm, but it was distributed unevenly. There was a 15-cm void at the top of 70009, a 2-cm void at the top of 70008, and an estimated 10-cm void in the top half of 70007 (the top 2 cm of 70007 were empty, and the next 16 cm were approximately half full of loose material, sloping from empty to completely full). Hence, recovery of actual material sampled is close to 100 percent. Stratal separation took place at the top of 70007; apparently, the soil of the upper two sections moved as a plug, possibly aided by air of pressurization entering through the connection between 70007 and 70008. In gross aspect, the deep drill core contains three major stratigraphic intervals: an upper, massive, coarse-grained interval dominated by basaltic and crystalline rock fragments; a middle, very-fine-grained interval dominated by anorthositic fragments; and a lower distinctly stratified interval containing a variety of breccias and crystalline fragments (fig. 7-27). The upper interval, which includes units 52 through 64, is 107 cm thick (from the lunar surface), characteristically massive and coarse grained, and more poorly stratified than the rest of the drill string. Principal layering occurs near the top and bottom of this interval. The uppermost 17.5 cm contain five layers (units 60 through 64), including a basal, fine-grained, thin bed that is overlain by 14.5 cm of fining-upward sequence. Conversely, unit 59, the major massive bed, is 61.5 cm thick and occupies the lower 7.5 cm of 70009, all of 70008, and the upper 16 cm of 70007. This massive unit is packed with poorly sorted rock fragments; in 70008, which has been dissected, these fragments show an upward succession from soil breccias, through massive to flaky, black, devitrifled glass, to fresh-appearing vesicular basalts and gabbroic anorthosites. Very little glass was found in this part of the core. Units 52 through 58 are fairly distinct and extend the coarsegrained interval to a depth of 107 cm. Basaltic and crystalline rocks are dominant at the top of 70006.

FIGURE 7-27.-interpretation of X-radiographs of Apono 17 deep drill string. The top of the drill string is represented by the abbreviation TDS. Depth values are direct from X-radiographs and therefore _re somewhat expanded.

Drive Tube 70012 (L52)
This core was hand driven to a hard layer at 28 cm depth 0.5 m inside the plus-Y footpad of the LM. The site lies on regolith developed on basaltic subfloor, near the center of the valley, approximately 750 m equidistant between the large (300 to 400 m) craters Camelot and Sherlock. The sample was collected in a relatively flat area with common, but subdued, 10- to 30-cm-diameter craters (ref. 7-42). Most of the surface appeared fine grained with particles near the limit of resolution of the surface photographs, but 1 to 2 percent of the surface was covered with particles as much as 3 or 4 cm in diameter. Similar material is in the core. Although this core was not disturbed by footprints (AS17-147-22517), the top 1 or 2 cm were probably depleted in fine soil by the LM descent propulsion engine. When the buddy secondary life-

FIGURE 7-28.-Block

of regolith historyface the vicinity section through Camelot in is a radial of deep drill string (LM area). The front Crater, the drill-stem site, and the LM site; the other faces parallel the standard lunar surface grid. (Vertical exaggeration is 200×.) support system (BSLSS) bag was opened in the Lunar Receiving Laboratory, the bottom cap of the core was off and lying nearby, and soil was spilling from the bottom. Forty-seven grams of slumped material were excavated from the base of the core to provide a fresh vertical face, which was then supported by a plug of aluminum foil. The upper follower was in place, and the X-radiograph indicated no serious cracking or slumping in the remainder of the core (fig. 7-29). The excavated material was mostly fines, with 5 to

PRELIMINARY Depth, cm Unit

EXAMINATION

OF LUNAR

SAMPLES

7-37

In all four units, the matrixappears besimilar, beingmoderately paque to o andrelativelygranular with

as much as 11 mm in sample is petrographically it is finer grained. or coarse-grained deep drill string

similar to the upper beds of 70008, None of the breccia fragments framework-textured soil of the

The sampling site lies near the base of a major scarp that crosses the Taurus-lAttrow valley. This site is approximately 50 m east of the 700-m Lara Crater and is surrounded by small, local craters. The largest of these craters, a moderately fresh 10-m-diameter pit, lies approximately 18 m northwest of the coring site, and several other craters over 5 m in diameter lie within 20 m. Small (as much as 1 m in diameter) craters are abundant, and the soil surface is fairly rough, with approximately 20-percent cover by 1- to 2-cm fragments (AS17-137-20981). A trench 20 cm deep near the 10-m-diameter crater revealed a medium-gray 0.5-cm surface layer over a light-gray 3-cm layer, which in turn overlies a medium-gray marbled or mottled zone that seems to be representative of subsurface softs in the light mantle.

appear in this core; however, the hard layer, which prevented further penetration, could be the coarsegrained deposit. If so, there is a deeper layer of fines on top of the coarse ejecta at this location. Nevertheless, the basaltic coarse fraction of 70012 parallels that of 70008, indicating a subfloor source for the upper soil layers,

Drive Tubes 73002 and 73001 (U31 and L45) A double drive tube was taken at station 3 to collect an undisturbed sample of the regolith developed on the light mantle. Although the lower drive

7-38 Much of 73002

APOLLO is permeated by

17 PRELIMINARY cracks (fig.

SCIENCE

REPORT with certainty. It

the only core that can be oriented

7-30), possibly caused by the wedging of large fragments into the drive tube or the spillage of 4 cm of soil onto the lunar surface. Whether or not these cracks have disrupted the stratigraphy is uncertain; at least two major stratigraphic intervals seem to be present on the X-radiograph, but there is no indication of the soil prof'de seen in the nearby trench. The material is coarse grained and massive with distinct rock fragments (probably subfloor basalt), reflecting expected surface conditions near local craters and within the Lara Crater ejecta blanket,

was driven into firm soil on an l l° slope to the south. The surface shows a 20-percent cover of moderately well sorted and rounded fragments as much as 4 cm in diameter (ref. 7-25) on fine-grained soils that are cohesive enough to retain the hole after the drive tube was extracted (AS17-146-22295). Subdued craters as much as 30 cm across are rare; one such crater, located approximately 1 m north of the sampling site, has abundant 3- to 4-cm blocks on the rim. Core 76001 is subdivided into four units on the basis of matrix content and the size and type of included rock fragments (fig. 7-31). Most rock fragments are indistinct, only slightly more opaque than the matrix, and probably represent anorthosites or breccias of massif origin; however, two large fragments in unit 2 are noticeably different. These

Drive

Tube

76001

(L48)

This single drive tube from station 6 is the only certain stratigraphic sample of massif regolith and is

APOLLO 17 PRELIMINARY SCIENCE REPORT obscured intervals contain black soft. Cloddy intervals occur in 74002 from 0 to 8, 14 to 20, 22 to 25.5, and 32 to 37 cm, including the upper 2 cm of 74001. The next 14 cm contain massive, nearly opaque (to X-rays) beds with slightly lower opacity at the base. The lowest 22 cm are massive, with subparallel lengthwise lineations of lower opacity, which may be fractures or steeply inclined bedding as observed in the trench. Approximately from the bottom 2 g of material were excavated of 74001 and examined under the

fragments are distinct in outline, are relatively opaque, contain abundant minute opaque particles less than 1 mm in diameter, and have 5- to 10-percent transparent circular areas as much as 2 mm in diameter; these features are typical of vesicular subfloor basalts. Except for the large vesicular rock fragments, this core is fairly fine grained and moderately well sorted, The relatively small surface craters at station 6 have contributed little to the massive, indistinctly stratifled upper 25 cm of the core. Rock types in the core, plus field evidence, indicate subfloor as well as massif contributions to this site, with massif source predominating. Possibly, the large, vesicular, presumably basaltic rock fragments in unit 2 were associated with a major cratering event large enough to propel basalt fragments from the valley to this point on the massif. The X-radiograph of this massif-derived soil is similar to those of the Apollo 16 drive tubes, probably because the anorthositic terrain of the massifs and the Descartes highlands produce similar soil-forming components. Both soils are (1) relatively transparent to X-rays, with a very sparsely granular matrix, (2) relatively low in distinct rock fragments, possibly because of the abundance of semitransparent anorthosites, and (3) extremely high in tiny opaque fragments of diverse shapes ranging fromdendritic to spheroidal, Drive Tubes 74002 and 74001 (U35 and L44)

binocular microscope. The material is unusually cohesive and consists of very dark to black opaque spheres and conchoidally fractured fragments. Drive Tubes 79002 and 79001 (U37 and k50) A double core was taken at station 9, which is approximately 70 m southeast and downslope from the rim of Van Serg Crater. Two fresh, sharp 1-m craters lie within 10 m of the coring site, and a subdued 60-m crater occupies the area 15 m west of the sampling area. Although lunar surface photographs indicate massive boulders on or near the rim of Van Serg Crater, the largest surficial fragments in the core area range from 20 to 2 cm (ref. 7-27), are poorly sorted, angular, and unfilleted, and cover less than 3 percent of the surface. A 12-cm trench approximately 1 m southwest of the coring site has medium-gray soft in the upper 7 cm but has light-gray to whitish soil in the lower part. The upper portion might represent "dark mantle" over the ejecta blanket from Van Serg Crater. However, this color change is not reflected in the X-radiograph of the drive tube, possibly because the core is permeated by fractures, which are undoubtedly a result of rocks being jammed into the coring device during sampling (fig. 7-33). DISCUSSION AND CONCLUSIONS

The double drive tube that sampled the contact between the orange and black soft on the southern rim of Shorty Crater was completely Idled with unusually dense soil (74001 was 2.35 g/cm 3 and 74002 was 2.00 g/cm 3) and was nearly impervious to X-rays. Consequently, rather mediocre X-radiographs were obtained even after near-maximum-intensity radiation. The clod-like layering encountered is shown in figure 7-32. It is hoped that these cores will preserve the spatial distribution of soils in the adjacent trench, where a surficial 0.5 cm of gray soil overlies an interval of orange soft, which, in turn, overlies black ilmenitebearing glass droplets seen in the top and bottom ends of the lower tube (ref. 7-26). Stratification in the upper tube consists of alternating layers of massive soil, impenetrable to X-rays, and very distinctly mottled soil that appears as poorly defined clods 0.3 to 3.5 cm in diameter. Presumably, the cloddy intervals contain orange soft, and the

The unit that partly filled and leveled the TaurusLittrow valley is mare basalt similar to that returned from Mare Tranquillitatis. Early studies of the ages of both the basalts and the orange glass (ref. 7-5) indicate that they are similar but slightly older than the Mare Tranquillitatis samples. Whether these sampies represent one or several flows is not clear (chemical data suggest at least two); but it is evident that widespread volcanism involving very-titaniumrich melts occurred over much of the eastern limb of

the Moon approximately 3.7 X 109 yr ago. Thus, the known timespan of mare volcanism, approximately 600 million years, remains essentially the same as before the Apollo 17 mission,

Breccias in various stages of crystallization appear to have been derived from several stratigraphic units present in the massifs. To date, the one reported breccia age from Apollo 17 of approximately 4.0 X

FIGURE 7-33.-Interpretation of X-radiographs of 79002 and 79001 drive tubes, The X-radiograph symbols axe the same as in figure 7-27.

109 yr (ref. 7-28) does not extend the rather restricted limits mentioned previously. Breccias range from those containing a high percentage of mineral and lithic debris with a small amount of interstitial

glass to those containing a small percentage of mineral and lithic debris in well-crystallized poikilitic textures. Problems still exist as to the extent of partial melting and the origin of the oikocrysts in the

latter breccias (refs. 7-29, 7-30, and 7-31). Detailed studies of the boulders that contain vesicles and vugs several centiments across, inclusions of one breccia in another, contact relationships between two breccia units, and the black dike that displays evidence of a chilled mar_n may help to answer these problems. The variety of breccia textures resulted from different extends of melting and different rates of heating and cooling associated with large masses of ejecta from major cratering events. The similarity of both major and trace component concentrations of the brown-glass matrix breccias from the Apennine Front, the recrystaUized breccias from Apollo 16, and the various crystalline breccias from Apollo 17 suggests that a genetic relationship may exist between these widespread breccias and KREEP-like chemistry. The occurrence in these breccias of clasts of plagioclase, olivine, and pyroxene similar to those of coarse-grained anorthositic and gabbroic rocks suggests that the latter formed the

source of the breccias and provides the interesting possibility that partial melting similar to that postulated for the production of KREEP-like melts (refs. 7-17 and 7-32) may be associated with large impacthag events that can produce large volumes of melt (ref. 7-33). Grieve and Plant (ref. 7-34) have reported an example of a breccia having gabbroic composition and containing interstitial melt and glass veins of KREEP-like composition. As was the case in past missions, the anorthositic rocks are generally crushed and recrystallized, thus obscuring the original textures. However, two coarsegrained norites and, at least one gabbroic rock with some areas of original texture should offer some insight into the chemistry and perhaps ages of the early crustal rocks. The occurrence of a large dunite clast in a boulder at station 2 suggests that the source material of the breccias must include coarse-grained segregations of magnesian olivine, thus providing further evidence for

PRELIMINARY an early complex crust composed of anorthositic,

EXAMINATION

OF LUNAR

SAMPLES

7-45

of a coarse-grained igneous gabbroic, and uttramafic

rocks. The "dark mantle" consists largely of the products produced by micrometeorite erosion of basalts, 5 to 20 percent of the orange and black glass found at station 4, and some tithic fragments derived from the massifs. The rather pure orange and black soils at station 4 suggest that there may be layers of these materials in the upper few tens of meters below the surface. If such layers are widespread throughout the valley, cratering events would be expected to excarate this material along with the basalts, producing the 5 to 20 percent of orange and black glasses found in the "dark mantle" soils. Anomalously high values of Zn and C1 for lunar soils and the relatively high Sr and Rb contents indicate that the orange glass is not directly related to the mare basalt melts, unless by some undefined complex fractionation scheme. Although the soils from the North Massif, the South Massif, and the light mantle are similar petrographically and appear in binary plots of major elements to be simple mixtures of basalts and anorthositic rocks, the trace elements indicate a more complex materials pattern. The South Massif and light mantle are considerably enriched in Zr and other

trace elements relative to the North Massif or to any mixture of basalts and anorthositic rocks. Thus, a KREEP component must be utilized to explain mixing models for the soils and the metamorphosed and partially melted breccias.

were to determine the physical characteristics and mechanical properties of the lunar soil at the surface and subsurface and the variations in lateral directions and to relate this knowledge to the interpretation of lunar history and processes. Data obtained on the lunar surface in conjunction with observations of returned samples of lunar soil are used to determine in-place density and porosity profdes and to determine strength characteristics on local and regional scales, The soil mechanics experiment on the Apollo 17 mission to the Taurus-Littrow area of the Moon was passive and involved no apparatus or crew time unique to the experiment. The preliminary analyses and interpretations presented in this report have been deduced from studies of extravehicular activity (EVA) transcripts and kinescopes, mission photographs, data on the lunar roving vehicle (LRV) performance, debriefings, and limited exaJNnation of returned lunar samples by the Lunar Sample Preliminary Examination Team (LSPET). SUMMARY OF PREVIOUS RESULTS

comparable gradation (silty fine sand). Particle-size distribution, particle shape, and relative density (ref. 8-2) control behavior. Soil porosity, density, and strength vary locally and with depth. Absolute densities may range from approximately 1.0 to 2.0 g/cm a, and values > 1.5 g/cm a are probable at depths > 10 to 20 cm. The relative density of the soil near the surface is extremely variable but is generally quite high (> 80 percent) below a depth of 10 to 20 cm. Although local (meter scale) variations in density and porosity exist, Houston et al. (ref. 8-3) and Mitchell et al. (ref. 8-4) have shown that the mean porosity at each of the Apollo sites from footprint analysis is approximately the same for the upper few centimeters of soil. Analysis by Costes (ref. 8-5) of vehicle tracks at £he same Apollo sites and at the Mare Imbrium site of the Soviet Luna 17 yields higher average porosity values at crater rims and other soft spots than for firm soiI located in intercrater areas. The soil on crater rims and on slopes appears to be more variable and, on the average,less denseand weaker than does soil in intercrater plains areas. Relative density (or porosity) is probably the most important single variable controlling strength, with most probable values of cohesion in the range of 0.1 to 1.0 kN/m 2 and friction angle in the range of 30 ° to 50 ° . The higher values are associated with higher relative densities.

The mechanical properties of lunar soil as deduced through the Apollo 15 mission were summarized by Mitchell et al. (ref. 8-1). The Apollo 16 results agreed generally with those of earlier missions and also provided more specific quantitative information on density and strength and their variability than was available previously. Even though lunar and terrestrial soils differ greatly in mineralogical composition, lunar

Soil mechanics data were derived from crew commentary and debriefings, television, lunar surface photographs, performance data and observations of interactions between soil and the LRV, drive-tube and deep drill samples, and sample characteristics as determined by the LSPET. 8-1

8-2

APOLLO 17 PRELIMINARY SCIENCE REPORT

Information from these data sources has been used in a manner similar to that from previous Apollo missions to deduce qualitative and semiquantitative information about soil properties. A statistical study of footprint and LRV track depths has been used as a basis for quantitative analysis of near-surface soil porosity. ]?remission orbital photographs and surface photographs have indicated a number of boulder tracks on the steep slopes of the North Massif and South Massif. These tracks have been analyzed by using the method of Hovland and Mitchell (ref. 8-6). Additional quantitative estimates have been based on LRV track depths and other specific observations as noted later in this section. RESULTS AND INTERPRETATIONS at the FIGURE 8-1.-Variable soil conditions in the vicinity of the surface electrical properties (SEP) experiment as evidenced by variabte depths of LRV tracks and footprints (AS17-141-21517).

General Soil Characteristics maurus-Littrow Site

Soil cover is present at all points visited in the Taurus-Littrow landing area. The surface is a similar color (gray and gray-brown) to that at the other Apollo sites, although lighter soil layers were encountered at shallow depths in some areas and orangecolored soil was exposed in a limited zone on the rim of Shorty Crater (station 4). Surface textures range from smooth areas almost free of rock fragments through patterned ground to areas heavily concentrated with larger rocks and fragments. Variability in soil properties is evident locally. Qualitative indications of this variability on a meter scale are provided in figures 8-1 to 8-3. Soil behavior during landing, walking, driving, and sampling was comparable to that observed during previous missions. Dust was readily kicked up under foot and by the LRV, tended to adhere to any surface with which it came in contact, and inhibited normal operations on several occasions. As readily apparent from the study of lunar surface photographs and from crew commentary, disturbed areas on the lunar surface appear darker than undisturbed areas, as has been the case at the previous landing sites. Subsequent crew observations of the landing sites from lunar orbit indicated that the disturbed areas were lighter than the undisturbed areas. This difference in appearance could indicate that the apparent changes in surface color caused by disturbance result from texture-related changes in albedo that influence the appearance when viewed

FIGURE 8-2.-Variable soil conditions in the light mantle at station 3 as evidenced by color differences (AS17-13821148). from different positions and at different Sun angles rather than from real color changes as a result of the exposure of new material. Alternatively, the different appearance might result from differences in scale between viewing from the surface and from orbit.

Both the postmission descent trajectory data and the crew comments indicate that the Apollo 17 descent was fairly rapid with vertical velocities of approximately 1 to 1.5 m/sec at altitudes of 60 to 70 m above the lunar surface, slowing to somewhat less than 1 m/sec at an altitude of approximately 15 to 20 m. The descent was accompanied by a fairly constant forward velocity of approximately 0.7 m/sec in the final 20 m of descent. Thus, the lunar module (LM) came in on an oblique trajectory similar to that of Apollo 14 (fig. 8-4). Previous analyses and mission results have shown that this kind of trajectory causes least disturbance of the lunar surface material during landing. In contrast, vertical descents, such as that of the Apollo 15 LM, generate substantial amounts of erosion. Blowing dust was first observed at a height of approximately 20 m above the lunar surface but caused no visibility difficulties during the final descent; in fact, the surface remained clearly visible all the way to contact, The descent engine was shut down approximately 1 sec after contact was indicated, and the LM dropped to the lunar surface while maintaining some forward velocity. The crew noted that the rear (-Z)

some crumpling of the Mylar insulation on the lower portion of the leg, indicating a possible stroking of 1 or 2 cm. This crumpling did not happen on any of the previous missions. From the photographs, no crushing of or damage to the footpad can be observed. As in the other landings, the descent engine exhaust swept the lunar surface in the vicinity of the landing site. Compared to adjacent areas, there were relatively fewer small rock fragments and soil clumps beneath the LM, although rocks 10 cm in diameter and larger remained. The crew observed that there v/ere clear indications of the interaction of the descent propulsion system exhaust gas with the lunar surface to a distance of approximately 50 m from the LM. From the crew's comments during sampling, the lack of blowing dust during the final stages of the descent does not appear to be caused by soil properties different from those experienced in prior landings. As noted in the subsequent sections, the grain-size distribution, cohesion, and density of the soil around the LM are similar to those previously established for lunar soil. This similarity tends to confirm previous conclusions that the amount of blowing dust during a landing is directly related to the descent trajectory and descent rate.

At the time this report was prepared, the LSPET had determined the complete grain-size distribution of 15 samples and the distribution of a small aliquot of the black soil taken from the bottom of the double core-tube sample taken at station 4. The results are shown in figure 8-5. These gradations are generally similar to those observed at previous landing sites. The band of 11 samples in figure 8-5 is slightly coarser in the coarse fractions than the composite distribution band for Apollo 1 1, 12, 14, and 15 (ref. 8-7), primarily because of the excess particles in the fraction that is > 10 ram. This observation was also noted for some of the Apollo 16 soils (ref. 8-4) and was attributed to the recent addition of coarse fragments that had not yet been worked into the soil matrix from the South Ray Crater event. Sample 71060 was taken at station 1 from beneath a slight overhang of a rock, and the crew observed that there were chips in the soil. The distribution for sample 74240, the gray soil found next to the orange soil, was changed considerably when the total sample was included, Despite the similarity of the grain-size distributions of the samples from various stations, the LSPET has found that the composition of the soil is highly variable in terms of proportions of basalt, breccia, mineral fragments, glass, and agglutinates. The softs from the massif stations appear to be derived from breccias, whereas much of the dark mantle on the plains was probably derived from basalts. The orange soil at station 4 is unique and is composed almost entirely of orange glass, A knowledge of particle composition is important for the interpretation of data from many lunar experiments because, at the same relative density, soils consisting of coherent particles are stronger and conduct heat and seismic signals better than soils composed of friable particles. Core Samples Drive Tubes.-Data on the drive-tube samples are summarized in table 8-I, and the sampling at station 6 is shown in figure 8-6. The bulk densities of the samples in the drive tubes as a function of depth in the lunar surface are presented in figure 8-7. In all instances, the density of the soil in the lower tube is greater than that in the upper tube; that is, density

zs0s0

,black s0, ,rein bottom of
stati°n4)

double coreat

0
0 10 I _ .1 Particleize,mm s I .01

FIGURE 8-5.-Groin-size distribution curves for several Apollo 17 samples. increases with depth, an observation consistent with findings at the Apollo 15 and 16 sites (fig. 8-7). However, the Apollo 17 core-tube densities (with the exception of the double core at station 4) are much more uniform with depth than were the Apollo 15 and 16 core-tube samples. The Apollo 17 core-tube densities tend to be higher near the surface and slightly lower below a depth of 20 to 30 cm than do the average densities for the Apollo 15 and 16 drive-tube samples. The high core recovery percentages at stations 4 and 6 and at the LM are comparable to those of the Apollo 15 and 16 samples for which the same type of core tube was used. The lower core recovery percentages at stations 3 and 9 indicate that the returned bulk densities will have to be corrected for sample compression. Densities in the double core from the rim of Shorty Crater at station 4 (2.03 to 2.29 g/cm 3) are distinctly higher than heretofore observed for any lunar samples. The upper tube contains orange-red soil with fine-grained black soil in the lower part. Black soil is exposed at the top and bottom ends of the lower tube. The orange soil, which is composed almost entirely of glass particles, is unusually cornpact and exhibits a high cohesion. A trench excavated into the material illustrates the high cohesion in the

aDetermined from X-radiographs, except as noted. bSample weights are +-4 g; better accuracy will be possible when _ubes are removed from stretch cans. CCorrected for voids. dCore sample vacuum container. eAssumed length. tCamera failure; photographs were blank. gEstimated from kinescopes. hCrew estimate. iEither 41 cm 3 of sample fell out of the top of the tube or the keeper compressed the top of the sample. The former is considered the more likely explanation; thus, density has been calculated accordingly. JApproximately 114 cm 3 fell out of tile bottom of the tube after it was placed in the sample collection bag because of a loose cap.

tbrm of a tendency chunks (fig. 8-8).

of the

material

to break

into

Unfortunately, the top of the soil column in the top three drill-stem sections, which were returned as a unit, moved approximately 15 cm, causing some loosening and disturbance. However, because the initial sample length is known, it is possible to estimate the initial average density for the top three drill-stem sections to be 1.99 -+ 0.05 g/cm 3, as shown in table 8-II. The bulk density as a function of depth in the lunar surface for the drill-stem samples is shown in figure 8-9. Values for the Apollo 15 and 16 deep dIill-stem samples are shown for comparison. Because the core recovery was nearly 100 percent, the measured bulk densities should be quite close to the in situ values. All the bulk densities are high; that of the second drill stem (2.11 g/cm 3) is remarkably so. The X..radiographs indicated this section to be quite gravelly, and dissection by the LSPET has confirmed this. This zone may be related to the hard layer encountered in the LM area at the end of EVA-3 where fourth a single core-tube sample was obtained. through the seventh drill stems all The have

The number of hammer blows (table 8-I), as indicated by the kinescopes, required to drive the core tube at station 4 was not exceptionally high compared to the driving earlier missions, indicating significantly less (or the resistance encountered on that tire porosily was not relative density higher) at

this location than had been previously encountered. Thus, the much higher bulk density is most likely caused by a higher specific gravity of the individual particles. Whereas the maximum reported value of specific gravity is 3.2 for an Apollo 15 sample (ref. 8-2), the soil in the lower half of the double core may have a value as high as 4. The black soil in the double core is composed primarily olivine phenocrysts, a trace of crystalline droplets, of glass, and 25-percent

ilmenite that has a specific gravity of 4.7. The LSPET has found that the black material is the first lunar soil studied thus far that contains no agglutinates, Drill Stems.-The deep core was drilled to a depth of 3.05 ± 0.01 m at a point approximately north of the Apollo lunar surface experiment 40 m package

(ALSEP) central station. Core recovery was 95 to 97 percent, and preliminary data on the eight drill-stem sections are given in table 8-II.

essentially the same density; the X-radiographs show uniformity as well. The absolute densities at the Apollo 17 drill site

FIGURE 8-7.-Bulk density as a function of depth in the lunar surface for drive-tube samples.

FIGURE 8-6.-Single drive tube at station 6. The drive tube has just been pushed to a depth of approximately 16 era. A special orientation mark is visible above and to the right of the numeral 8 on the tube. This is the only drive tube from Apollo 17 that has been positively oriented in the lunar surface. After this photograph was taken, the drive tube was hammered to a final depth of 37 cm (AS17146-22291).

FIGURE 8°8.-Trench excavated into orange soil on rim of Shorty Crater at station 4. The chunky texture reflects the high cohesion of this soil (AS17-137-20989).

are generally higher than those measured at the Apollo 15 and 16 drill sites, and the distribution of densities as a function of depth suggests a depositional history entirely different from either of the previous two sites. The average drill rate of the first Apollo 17 heat flow borestem was approximately 70 cm/min, indicating that the relative density at the the Apollo 17 site is considerably higher than that at Apollo 16 site. If the later borestem design of Apollo

16 and 17 had been available, the predicted drillrate at the Apollo 15 site would have been the same or slightly less than that measured at the Apollo 17 site, indicating that although the absolute densities in the Apollo 15 drill stem were less than those of Apollo 17, the relative densities were generally the same or higher. This indication implies a significantly different soil composition. Even though the relative densities at the Apollo 17 drill sites were indicated to

aTotal weight is 1772.5. bDetermined by X-radiography. CBased on a sample diameter of 2.04 cm. dTotal length is 292 ± 2. eCore-tube rammer-jammer was inserted to a depth of 30 +-2 cm before drill stem was withdrawn from soil. fApproximately 2-cm void at top of stem. gApproximately 6-cm void at top of stem. hNominal length is 42.5 cm; 0.5 cm fell out of bottom of drill stem on lunar surface. 0 I I i I I I not uncommon for the lunar surface and that the soil near the surface are also

I....

1
_t l_ _l __

I

soft.

Softer

soil conditions

100 E"

t._., ,.I 16! , Apollo i t...., I I t_ "--" Apollol5 / ....

indicated for the Apollo 16 site by the porosity as at the Apollo analysis may have been anomalously determined by 16 site of footprint depths and LRV tracks (ref. 8-1). After extraction of the drill stem, the neutron flux probe was inserted to a depth of 2.1 m (length of probe) in the vacated hole. Before insertion of the probe, it was noted that the hole was intact and flared at the top. No resistance to insertion of the probe was encountered, except at approximately one-third the depth where a slight obstruction was noted. This resistance may have coincided with the i 2.5 location of the gravel layer. There was no noticeable resistance to withdrawal of the neutron flux probe at the end of EVA-3, at which time it had been in the ground for 49 hr. This suggests that there was no caving or squeezing of the soil under the increased shear stresses caused by the presence of the hole, in agreement with premission predictions. A stability analysis of the open drill hole provides lower bound estimates of the soil strength parameters as shown by Mitchell et al. (ref. 8-8). In that report, the horizontal scale in figure 7-24 is in error. A corrected plot of the relationship between soil cohesion and friction angle and the depth to the bottom of the elastic zone in an open borehole is given in

_' =_ _2oo

Apollo 17

"7 l !

3°_.0

t I 1.5 2.0 gulkdensity, g/cm 3

FIGURE surface for drill-stem as a function of depth in the lunar 8-9.-Bulk density samples.

be generally

quite high, the observed

drill rates were

quite variable and reflected hard and soft layers at depth, After the easy drilling experiences of Apollo 16, it was assumed that the hard drilling encountered at Apollo 15 was exceptional. On the basis of three data points, it must now be concluded that hard drilling is

8-8

APOLLO 17 PRELIMINARY SCIENCE REPORT Although the open holes remaining after extraction of the drill stem suggest quite high strengths for depths of approximately 2 m at both the Apollo 16 and 17 sites, strengths of this magnitude are not commonly encountered at shallow depths as indicated by the values determined by penetrometer testing at the Apollo 16 site (ref. 8-1). Boulder Tracks

figure 8-10. Below the depth corresponding to any given combination of friction angle and cohesion, a plastic zone should develop, and there should be soil yielding that would lead to closure of the hole by inward squeezing of the soft. If no yielding of the soil developed to a depth corresponding to the length of the neutron flux probe (and little could have occurred because the probe diameter is only slightly less than the hole diameter), then the required strength parameters are as indicated by the vertical line in figure 8-10 at a depth of 2.1 m. Even for high friction angles (> 50°), a soil cohesion exceeding 1.0 kN/m 2 is required. Strength parameters of this magnitude are likely only for conditions of high relative density and would be consistent with the hard drilling discussed previously. High strength is not required for the full depth of the hole. Stability can be maintained for conditions of strength increasing with depth to satisfy figure 8-10 at any depth,

2.5 Friction angle=30* 2.0 1.5 . o= 1.0 I o 40° 50 °

More than 300 tracks made by boulders rolling, bouncing, and skidding down lunar slopes were identified by Grolier et al. (ref. 8-9) in the Lunar Orbiter photographs. The Apollo 17 mission provided the first opportunity for a close study of these interesting features because many tracks can be seen on the Taurus-Littrow hills. Unfortunately, prints of the 500-mm lunar surface photographs, which permit the most detailed study of the tracks, were not available to the soil mechanics team during the preparation of this report. Hence, the analyses, based mainly on 60-mm and premission orbital photographs, are tentative, and the results are subject to subsequent refinement. In a qualitative sense, boulder tracks serve as exploratory trenches and can provide the relative sharpness of track features provides some indication of soil movement after track formation. Quantitative analysis of boulder tracks, from which information can be derived relating to soil information about regolith thickness and history, and strength and density, is possible. Studies of this type al. (ref. 8-11), Moore (ref. 8-12), Moore et al. (ref. have been reported by Filice (ref. 8-10), Eggleston et 8-13), and Hovland and Mitchell (ref. 8-6) for boulder tracks found in Lunar Orbiter photographs. The method in reference 8-6 is used here. An oblique closeup view of a larger boulder and its associated track visited at station 6 on the south slope of the

FIGURE 8-10. Depth to bottom of the elastic zone in an open borehole as a function of soil strength parameters,

FIGURE 8-11.-Partial panorama at station 6 showing a laxgeboulder and the track down which it rolled (AS17-141-21582,21584, 21586, 21590, and 21594).

SOIL MECHANICS North Massif during EVA-3 is shown in figure 8-11. Several tracks were located on the premission orbital photographs of the East Massif and the

8-9

Sculptured Hills; their locations are indicated in figure 8-12. Several tracks on the South Massif are identified in figure 8-13. Additional tracks on the

L.__..J 530 m

.....

Boulder tracks

FIGURE 8-12. Locations of boulder tracks on the East Massif and on the Sculptured Hills. For tracks identified by a letter, a definite causative bouhler could be located; for tracks identified by a number, only the most probable causative boulder could be located.

8-12

APOLLO 17 PRELIMINARY SCIENCE REPORT

.......

Boulder tracks

FIGURE 8-15.-Boulder tracks on the North Massifas seen from the LM (track identifications are the sameas for fig. 8-12) (AS17-147-22502).

and is used with a bearing capacity equationadapted to the case of a rolling sphere. The resulting relationships between soil friction angle, slope angle, and track-width-to-boulder-diameter ratio are shown in figure 8-16. A soft density of 1.6 g/cm 3 and a cohesion of 1 kN/m 2 were assumed. This value of cohesion is near the upper end of the range of cohesion values determined for the lunar soil thus far (refs. 8-1 and 8-4). The effect of an overestimation in cohesion by as much as a factor of 10 will lead to an underestimation of friction angle of only 1° to 2 °, however. An estimate of the variations in friction angle that are likely to result from errors in a measurement of track depth and width and in boulder size has been made (ref. 8-6). The analysis indicated that friction could differ by as much as-+ 2° because of measurement errors. The frequency distribution of the soil friction angles derived from the boulder track data is shown in figure 8-17 and is generally compatible with the soil gradations, densities, and porosities found at other locations on the Moon. Although the range is similar to that determined by other means (refs. 8-1 and 8-4), the most frequent values are somewhat less than would be expected because tracks of the size analyzed must involve considerably greater soil depths than for the other determinations. This difference may reflect limitations in the analysis,

Thus, the variability indicated by figure 8-17 is considered more reliable than the absolute values of friction angle. Surface Soil Porosity Deduced from

Footprint Analysis Previously developed methods (refs. 8-3 and 8-4) have been used to extend the statistical analysis of lunar soil porosity as deduced from footprint depths to include the Apollo 17 site. The curve correlating footprint depth with average porosity and relative density of the upper few centimeters of the lunar surface, based on results of model test and theoretical analyses (ref. 8-14), is shown in figure 8-18. A total of 144 different footprints from the Apollo 17 photographs were analyzed, and the results are summarized in table 8-IV. A histogram showing all data for Apollo 17 is presented in figure 8-19. Also summarized in table 8-1V are results for previous Apollo missions. For the Apollo 17 site, only three footprints on crater rims were analyzed. This sample size is too small to characterize crater rims statistically; thus, the values shown in table 8-IV are essentially applicable only to intercrater areas. The data in table 8-IV show that neither the intercrater average porosity (43.4 percent) nor the standard deviation (2.4) differ significantly from the

letter, a definite causative boulder could be located; for tracks identified by a number, only the could be located. Apollo sites. The Apollo slightly higher. The Apollo 17 also compare average values for all and 2.75) and the unand 2.55). The unby computing a simple averages for each site of observations at any one site. Conversely, the weighted average porosity (44.0 percent) is weighted heavily in favor of Apollo ]6 where an unusually large number of footprint observations was possible. Thus, the unweighted values (43.5 percent and 2.55) probably represent a better estimate for a randomly selected location on the lunar surface. No distinguishable difference in porosity was found between the Apollo 17 traverse stations and

average porosity and relative density in the top 10 cm of the lunar surface. Average porosity is based on a 58.3-percent print depth maximum and a 31-percent minimum. assumes a contact stress of 7 kN/m _ . Foot-

TABLE

8-IV.

Results Deduced

of Statistical from Foot

Analysis ;rint Depths

of Porosities

Location

No. of observations

Mean porosity, percent

Mean a Standard deviation relative density, percent

Apollo 17 site All data LM and ALSEP area All traverse stations Intercrater Apollo areas 11

APOLLO 17 PRELIMINARY SCIENCE REPORT S0ilmodel B (h =35° c o0.17Nlm k 2 k = 0.81NIcm 3 _c 0.35Nlcm @ n = 1.0cm K : 1.0 EVA-3 ' I' I I '_'-I "1 I From these parameters, pull as a function of slip and torque as a function of slip relationships were calculated using analytical expressions developed by Bekker (ref. 8-21). These expressions were then used as computer input data, together with other information relating to the mission, terrain, and vehicle characteristics, to calculate the LRV energy consumpBecause site (ref. 8-19). tion at each of the small amount of wheel sinkage, the LRV wheel/soil interaction with the lunar surface

(table 8-V) on the basis of in-place plate shear tests performed on a lunar soil simulant (refs. 8-15 and

Apollo 16 _ EVA-3 I '1' t i EVA-3 o c_

i

EVA-1 EVA-2 20_ _'-"t "'""_'_ I
EVA-I

t EVA-2

angle valueswith the average Ganalysis of LRV tracks deduced from the values deduced from consistent 8-16). tracks (table 8-V). coefficients k c and k4_ are The values of Finally, based on other lunar LRV soil mechanics observations and measurements (e.g.,

40I, .l, _> 20 _ f_ 0 I 5

t t I I 10 15 20 25 Distance traversed, km

_ 30

_ 35

value of 0.17 kN/m 2 for the top surficial material was adopted. soil erosion during LM descent), an average cohesion In general, the soil/LRV interaction data support the conclusion that the surficial lunar soil is less compact, more deformable and compressible, and has lower strength than does the subsurface material.

FIGURE 8-21.-Measured energy consumption of the LRV in relation to the predicted values based on the soil properties indicated. core-tube samples. As shown in figure 8-21, the same soil model, which had been based on Surveyor data for soil near the surface (ref. 8-20), yields results that closely agree with the measured LRV energy consumption at both the Apollo 16 and 17 sites, In figure 8-21, the symbols q_ and c designate, respectively, the soil friction angle and cohesion;K is a normalizing constant conditioning the amount of shear strength and the thrust mobilized by the soil at a given wheel slip; and ks, kc, and n describe the pressure-sinkage characteristics of the soil under wheel loads(ref. 8-21). k p = ¢

Downslope Movements Caused Meteoroid Impacts

by

Houston et al. (ref. 8-22) have assessed the relative importance of vibrations induced by meteoroid impact as a mechanism for mass movement of lunar soil downslope. The seismic energy generated by impacts of various-size meteoroids was estimated, and the associated incremental movement was computed for each impact. Movements were summed over the range in meteoroid sizes producing significant movement, both with respect to distance from point of impact and with respect to time, using meteor flux rates derived by Gault (ref. 8-23) with an adjustment based on more recent estimates of the age of the Moon. The results indicated that the flattest slope on which significant cumulative downslope soil movement of approximately 1 m is likely to have occurred because of impact-produced ground accelerations is approximately 25 °. The flattest slope on which cumulative downslope movement of several hundred to a few thousand meters is likely to have occurred is approximately 48 °. Because of the great length of

+ k@zn

(8-2)

in which p is the wheel contact is the wheel footprint width in wheel sinkage in centimeters. If pressure-sinkage relationship is

pressure in N/cm 2, b centimeters, and z is for a given wheel the linear (n = 1), the

coefficients k c and k4, are analogous to the penetration resistance gradient of the soil G.

SOIL MECIIANICS most of the highland lunar slopes, it is estimated that downslope movements of a few thousand meters would be required to cause flattening of the slopes by as much as 1° or 2 °. Thus, it appears that only on very steep lunar slopes could there have been significant downslope soil movements caused by shaking from meteoroid impacts alone, and that large-scale slope degradation must have developed primarily by other mechanisms. However, this conclusion does not mean that soil movement, once triggered by meteoroid impact, could not continue as a result of changes in strength properties of the soft mass or fiuidization, Origin of the Light Mantle It has been hypothesized (ref. 8-24) that the light mantle that extends outward over the plains area north of the base of the South Massif (fig. 8-22) originated as an avalanche from the slopes of the

8-19

South Massif. A study of stereographic photographs obtained from orbit during the Apollo 17 mission using the panoramic camera gives some indication of a scarp on the South Massif that could define the boundary of a slide mass. Furthermore, according to the LSPET, the light mantle material on the plains appears to be compositionally similar to that from the South Massif. Thus, reasonable evidence exists that a slide or avalanche did occur. If a slide did occur, then an important question to be resolved is the mechanism by which the material spread out onto the valley floor and came to rest with a nearty level surface. As the slope of the South Massif is only approximately 25 ° to 30 °, meteoroid impact is unlikely to have been able to do much more than just initiate movement. Incremental movements accumulating from impacts alone could not account for the magnitude of movements indicated. However, once a

FIGURE 8-22.-Orbital view of the Apollo 17 landing: area. The light mantle to the north of the South Massif may have been an avalanche produced by the mechanisms proposed in text. A possible slide scarp can be seen located as indicated on high-resolution panoramic camera photographs (Apollo 17 panoramic camera frame AS17-2314).

8-20

APOLLO 17 PRELIMINARY SCIENCE REPORT those of the soils at the previous Apollo sites. Although no crew tasks or lunar surface measurements were done specifically for the purpose of obtaining quantitative soil mechanics data, a number of preliminary analyses and interpretations have been made using EVA transcripts and kinescopes, photographs, data on soil/LRV interactions, debriefings, and limited examination of returned lunar samples. The following specific conclusions have been developed. 1. Soil cover is present at all points visited in the Taurus-Littrow landing area. Surface textures and colors are similar to those at the other Apollo sites. 2. There is considerable local (meter scale) variability in soil properties. 3. Particle-size distributions of samples from different traverse stations are generally similar to each other and to those observed at previous landing sites, even though soil compositions are highly variable among the stations in terms of proportions of basalt, breccia, mineral fragments, glass, and agglutinates. 4. The drive-tube samples indicate some increase in density with depth but more uniformity with depth than the Apollo 15 and 16 samples. Soil density in the double drive tube taken on the rim of Shorty Crater (station 4) is higher than heretofore observed for any lunar sample. The presence of high specific gravity particles, such as ilmenite, is a more probable cause than is very low porosity. 5. Absolute densities at the Apollo 17 drill site are generally higher than those measured at the Apollo 15 and 16 drill sites, and the distribution of densities with depth suggests a different depositional history from that at the previous two sites. 6. Stability analysis of the open drill-stem hole, into which the neutron flux probe was placed and removed without soil resistance, indicates that there was little or no squeezing or caving of the soil during a 49-hr period and that soil strength at a depth of 2 m must have been considerably greater than the average strength near the surface. 7. Tracks caused by the rolling and bouncing of boulders are common on the slopes of the massifs and the Sculptured Hills. A frequency distribution of soil friction angles was deduced from rolling boulder track data that is consistent with the soil gradations, densities, and porosities found at other locations on the Moon, although the absolute values of friction angle were computed to be somewhat lower than was anticipated. 8. Near-surface soil porosities deduced from foot-

slide was triggered, if the soil strength were to decrease significantly or if the mass became fluidized because of the generation or liberation of significant quantities of gas, then continued movement might be possible, In the analysis of downslope movements referred to previously, no change in soil strength was assumed once failure occurred. The nature of lunar soil particles, particularly the agglutinates and breccias, is such that particle breakdown during shear is likely, The results of strength and compression tests on lunar soil samples by Carrier et al. (ref. 8-25) suggest that particle breakdown does indeed occur. Mitchell and Houston (ref. 8-26) found that decreasing tire particle size of a basalt lunar soil simulant resulted in a significant decrease in the angle of internal friction. It is not likely, however, that particle comminution could lead to a decrease in friction angle to a value less than 25 °, which would be required to result in any slope flattening on the South Massif. A loss in strength caused by a friction-angle decrease sufficient to allow spreading of the material over the level plains does not seem possible, The plausibility of fluidization as a mechanism hinges on the generation or liberation of sufficient gas during the initial stages of movement to provide a sufficient uplift pressure on the overlying soil to reduce or eliminate frictional resistance to downslope movement. Gas of solar wind origin was liberated in the compression and strength tests described in reference 8-24; however, the amount was too small by orders of magnitude to cause fluidization. Conversely, other investigators have generated gas by a combination of grinding and heating, Clanton et al. (ref. 8-27) and Bogard et al. (ref. 8-28) have confirmed that agglutinates are enriched in solar wind and thus could serve as a source of gas when broken down. The Apollo 17 soil composition analyses indicate that the samples from the massifs contain greater proportions of breccias, approximately the same proportion of agglutinates, and less basalt than does the dark mantle material on the plains. Thus, a fluidization mechanism may be tenable to account for the origin of the light mantle, whereas flnidization would be very unlikely if the massifs were composed only of ground-up basalt, CONCLUSIONS The physical and mechanical properties of the soil at the Apollo 17 landing site are generally similar to

SOIL MECHANICS print depths indicate that neither the intercrater average porosity nor the standard deviation differ significantly from the average values for previous Apollo sites. The average relative density for all Apollo landing sites, as deduced from 687 observations of footprint depth, is approximately 66 percent. Large local (meter scale) variations exist in porosity and relative density. 9. The LRV performance, including slopeclimbing capability and power consumption, was within the predicted limits. Analysis of track depth, shape, and texture indicated no discernible variations

in the average consistency of the surface soil throughout the Taurus-Littrow region or relative to the Apollo 14 through 17 and Luna 17 landing sites, although variations about the average existed on a small scale at all sites. o 10. Only on very steep lunar slopes ('> 25 ) could there have been significant downslope soil movements caused by shaking from meteoroid impacts alone, and large-scale slope degradation must have developed primarily by other mechanisms. 11. There is evidence to support an avalanche as tile origin of the light mantle covering the plains north of the South Massif. Fluidization of the soil mass by gas pressures generated during the initial phases of soil movement would be required to account for the large-scale movements observed. Finally, soil mechanics data from all the Apollo missions support the general conclusion that processes affecting the entire lunar surface, such as meteoroid impact and the solar wind, control the average relative On the the soil properties such as grain-size distribution and density, which are nearly the same at all sites. average, the soil on slopes is less dense than on level areas because of the effects of

downslope movement. Local geology and topography on a small scale and specific cratering events appear to control the variations about the aw_rage to the extent that the standard deviation can be relatively large.

The objectives of the heat flow experiment (HFE) were to make a direct measurement of" the vertical component of heat flow from the hmar interior through the surface and to determine the thermal properties of the upper 3 m of the lunar regolith, The age of the Moon is placed at 4.6 X 109 yr. For a planetary body as small as the Moon, much of the initial heat energy has been lost to space since formation. Even if the Moon were initially at molten temperatures, the present flux at the surface would be small. The major contribution to the surface heat flow comes from heatgenerated by the disintegration of long-lived radioisotopes of uranium (23SU and 238U), potassium (4°K), and thorium (232Th). Thus, the present surface heat flux reflects the abundance of these isotopes to a depth of approximately 300 kin, or 43 percent of the volume of the Moon. It is now certain that extensive differentiation occurred during the early history of the Moon that would concentrate these isotopes in the outer shells. In this case, the present surface heat flow wouhi very nearly indicate the total abundance of these isotopes, More than 5000 heat flow determinations made on Earth show the average global flux to be 6.3 X 10-6 W/cm 2 (ref. 9-1). (Throughout this report, W-secwill be used as the unit of heat energy. Other commonly used units are the calorie, which equals 4.18 W-sec, and the erg, which equals 10 ? W-sec. The average Earth heat flow is 1.5 X 10 -6 cal/cm2-sec and 63 ergs/cm2-sec.) Urey (ref. 9-2) pointed out that the total rate of heat flow from the Earth is essentially equal to the total rate of heat production in the Earth if it were constituted of materials with chondritic abundances of uranium, potassium, and thorium, However, Gast (ref. 9-3) showed that Earth rocks were strongly depleted in potassium relative to solar aLamont-DohertyGeologicalObservatory. bH.H. LehmanCollege,City University of New York. tPrincipalInvestigator, 9-1

and chondritic abundances, which led Wasserburg et al. (ref. 9-4) to propose that, to explain the heat flow from Earth, a higher abundance of uranium (nearly 3 times that of chondrites) is needed. They estimated a uranium abundance of approximately 30 ppb for the Earth. The large variations of heat flow observed over the surface of the Earth are principally related to the present tectonism of the Earth lithosphere (ref. 9-5). The largest variations are observed at extensional and compressional boundaries of vast lithospheric plates that are moving relative to each other. Seismic observations (ref. 9-6) and the preservation of ancient surface features on the Moon demonstrate that no comparable tectonic movements have occurred on the Moon for the past 3 X 109 yr. The Moon is tectonically dead compared to the Earth; therefore, any variations in surface heat flow over the surface should reflect either deep-seated changes in abundances of radioisotopes or in convective patterns in the Moon. Because of the static nature of the outer crust of the Moon, heat flow determinations at a single location might be quite representative of a very large region of the Moon if local surficial effects such as refraction by conductive inhomogeneities and topography are properly accounted for. Numerous attempts have been made to determine the surface heat flow from the Moon by detecting thermal radiation from the Moon in the microwave band. Because of the partial transparency of lunar surface material, energy with wavelengths greater than I mm received at Earth-based antennas originates in the subsurface and contains information on subsurface temperatures. By making estimates of thermal and electrical properties, the heat flow can be determined from the change of brightness temperature with wavelength. The earliest heat flow determination was that of Baldwin (ref. 9-7), who estimated an upper limit of 1 X 10 _6 W/cm 2. Russian investigators estimated the heat flow to be very

9-2

APOLLO 17 PRELIMINARY SCIENCE REPORT T is the temperature, z is the depth, and the constant k m is the thermal conductivity. The negative sign indicates that the heat flows in a direction opposite to the increase of temperature. The experiment is designed to measure accurately the vertical temperature gradient in the lunar soil to a depth of 2.3 m. Surface temperature measurements are also made that can be used to deduce the thermal properties of the upper 10 to 15 cm of regolith. In situ measurements of thermal conductivity of the regolith at depths where the gradient is measured are also performed. Two measurements of heat flow at locations separated by approximately 10 m are made to detect possible lateral variations. The essential parts of the heat flow instrument are two identical temperature-sensing probes. Each probe consists of two 50-cm-long sections (fig. 9-1(a)). In each probe section are two platinum resistance bridges; each bridge consists of four 500-ohm iliamentary platinum elements interconnected by Evanohm wire (fig. 9-1(b)). Opposing arms of a bridge are wound together in a single sensor housing;two sensor housings, comprising a complete bridge, are mounted at opposite ends of a probe section. Voltage measurements on a bridge can be interpreted by accurate calibrations in terms of average bridge temperature Ta and temperature difference AT between sensors. The temperature at each sensor is simply determined from Ta +- 1/2 AT. The accuracies of the HFE temperature measurements are given in table 9-I. The cable thermocouples consist of a string of four Chromel/constantan junctions embedded in each probe cable. The lowermost junction is positioned inside the gradient sensor housing at the top of the probe. The reference junction for each cable is inside the electronics housing and is mounted in an isothermal block with a platinum resistance thermometer (the reference thermometer). The thermocouple (TC) circuit is shown in figure 9-1(c). The accuracy of the thermocouple measurements has special significance for interpreting the subsurface temperature profiles at the Apollo 17 site. Therefore, certain features of the thermocouple measurement, which affect the accuracy, should be described. First, only the Chromel/constantan junction (TC 1) inside the topmost gradient is coupled with the reference junction during a measurement sequence. Junctions TC2, TC3, and TC4 are coupled with TC1 so that, in effect, TC1 becomes the reference junction and the

nearly equal to that of the Earth, based on a very careful set of radio-telescope observations in the wavelength band 3 to 50 cm (ref. 9-8). These same measurements were later revised by using different thermal properties and a layered model to give heat flows in the range 3 × 10 _6 to 4 × 10 -6 W/cm 2 (ref. 9-9). During the Apollo 15 mission, the first direct measurement of heat flow through the lunar surface was made at Rima Hadley (lat. 26006 , N and long. 3°39 ' E). A second measurement was made during the Apollo 17 mission at the Taurus-Littrow site Oat. 20°10 ' N and long. 30046 , E). At Taurus-Littrow, two probes to determine heat flow were emplanted approximately 11 m apart. Analysis of data taken during the first 45 days after emplacement indicates that the heat flow is 2.8 X 10 -6 W/cm 2 (0.67 /lcal/cm2-sec) at one probe location and 2.5 × 10 -6 W/cm z (0.60 /_cal/cm2-sec) at the second probe location. For comparison, the value measured at Rima Hadley is 3.1 × 10 -6 W/cm 2 (0.74/lcal/cm 2sec). The Rima Hadley measurement and TaurusLittrow probe 1 measurement have an estimated error of -+20 percent. The probe 2 measurement at Taurus-Littrow has a slightly larger uncertainty because the heat flow appears to be locally disturbed, These measurements have not been corrected for local topography, EXPERIMENT Experiment DESCRIPTION

Concept and Design

The concept on which the HFE is based is the direct measurement of the vertical flow of heat through the regolith. Tire measurement should be made far enough below the surface so that the time-varying heat flow resulting from the very large diurnal variations of surface temperature is small compared with the flow from the interior. At Taurus-Littrow, this depth is approximately 100 cm. Below this depth, the increase in temperature with depth results principally from the hotter lunar interior. The outward flow of heat is directly proportional to the rate of temperature increase with depth, These quantities are related by the equation Fa = -km(dT/dz) where F z is the vertical component of theheat (9-1) flow,

HEAT FLOW EXPERIMENT 120 Current sense

9-3

__ lr .siml
Heatert sensor sensor

supply

Lower I..-"k

.._'-'"i "upper <_

lop-Gradient bridge Ring bridge 80 Upper section

,sensor.--[

%/

vensor-,

_ TOmultiplexer (b) Typical platinum resistance bridge circuit.

/ .Constantan .;_!_
I I -_

.Kovarwire ,,,'_'
1141

--i---a--l-',

,, L r
i I

A •

Ii = I

mplifier

Chromel ....... Thermocouple 4 I TC2 Heater2 \

a. I I .:.' / ' -/" tEvanoh m _'_ Platinum

t

Reference I

TC4 Heater 3 TC1

./-

-IReferencel -

Isothermal 1 bridge I block _ (c) Thermocouple circuit.

4(3top gradient sensor becomes the reference thermometer. Because the temperatures of TC3 and TC4 are much closer to that of TC1 than to that of the thermometer in the electronics box, the calibration errors are reduced by this technique. Second, the placement of junction TC1 inside the gradient sensor on the Moon. Thus, an in situ calibration of the thermocouple circuit against the much more accurate gradient permits asensor iscomparison direct performed. between the two sensors Conductivity experiments are made using 1000ohm heaters that surround each of the gradient sensor housings. The experiments can be operated in either _x,._ of two modes by 0.5 W, depending rounding regolith. lunar material at power was used experiment. After energizing the heaters at 0.002 or on the conductivity of the surBecause of the low conductivity of Taurus-Littrow, only the lower for the Apollo 17 conductivity initiation, power is left on for 36

where c I and c2 are constants. The form of equation (9-5) is the same as that for a heated infinite cylinder in an infinite homogeneous medium at long times (i.e., > 20 hr for a cylindrical source with a radius and heat capacity per unit length probe/borestem system) (ref. 9-13). For an infinite cylindrical source c 1 = Q/4"gkm of the HFE

\
\ \ \ .a4

\
.02

where Q is the power per unit length in W/cm. Thus, cl depends solely on the heater power per unit length and on conductivity. The constant c_ can be determined easily because it is the slope of the temperature rise curve when plotted versus In t; therefore, cylindrical sources are often used as a practical technique for measuring conductivity. Conductivity is determined from lunar experiments by comparing observed slopes on a logarithmic time scale with values of cl calculated with the finite difference models. Parametric studies, in which certain thermal properties are varied singly in the numerical model, show that for times > 20 hr, cl i's very nearly insensitive to changes in pc of the surrounding medium, changes in borestem conductance, and changes in the thermal links between the probe and borestem and the borestem and lunar medium. However, cl is sensitive to changes in conductance in the probe body, which can alter the flow of heat from the heater axially along the probe. Assumptions of thermal properties in the numerical models that influence axial heat transfer along the probe are probably the largest source of error in the conductivity determinations. The similarity in performance of the lunar conductivity experiment and of an infinite cylindrical source is principally due to the relatively efficient flow of heat axially along the borestem. Even though the probe heater is very short (1.9 cm), it heats a section of borestem that is long compared to the borestem diameter. For times > 20 hr, the isotherms in the surrounding medium are roughly cylindrical in the vicinity of the heater as shown in figure 9-2. The numerical computations also show that the experiment is most sensitive to lunar material within approximately 5 cm of the borestem wall.

FIGURE 9-2.-The geometry of the probe, borestem, contact zone, and lunar regolith in the vicinity of a conductivity experiment. The dashed lines show surfaces of equal temperature rise in kelvins after the heater has been on for 36 hr. The model parameters are km = 2.4 X 10-4 W/cm-KandH_ = 1.5 X 10-4 W/cm2-K. The effective conductance of the contact zone has a pronounced effect on the magnitude of the sensor temperature rise at any given time. Because k m can

and Its Effect at Depth Lunar surface temperatures vary nearly 300 K parameter before can be dawn to lunarbY matching determined from just and lunar noon. This variation induces subsurface variations that propagate downward as thermal waves. For a homogeneous medium of diffusivity a with a sinusoidal variation A o cos wt at the surface, the temperature at a given depth z is given by T(t,z) = Aoe-6Zeos(_t - _z) (9-7)

Depth, cm (a) The attenuation of the peak-to-peak amplitude of the diurnal and annual temperature with depth in the regolith. The 6 in each equation is the effective decay constant deeper than 20 cm.

where Ao is the amplitude of the surface variation in degrees, w is the angular frequency in rad/sec (2.5 × 10 6 for the diurnal variation and 2 X 10 7 for the annual variation), and 6 = _, cm-1 (9-g)

2,r

1.51r

Equation (9-7) indicates that the variation decreases in amplitude by a factor e- 1 and is delayed in phase 1 rad for every _-1 centimeters of depth. The propagation of surface temperatnre variations into the lunar regolith is more complex :for a number of reasons. First, the surface variation is not a simple sinusoid but contains significant higher harmonics. Second, thermal properties vary signiticantly with depth; and third, radiative transfer, which depends on I "3, plays an important role in the upper few centimeters of the lunar soil. It is necessary to resort to numerical calculations that include these complications to determine the expected temperature variations in the subsurface. In figure 9-3, the peak-topeak attenuation and phase lag of the diurnal variation are shown as a function of depth for the conductivity profile at the Apollo 17 heat flow site. The upper part of the conductivity profile is derived from surface temperature measurements that are described in the section entitled "Surface Temperatures Deduced From Whermocouple Measurements." For depths greater than a few centimeters, the amplitude decreases in a simple exponential fashion, as evidenced by the nearly straight line on a semilogarithmic scale. Similarly, the phase lag shows a

" _ g-

.5_ ] _ Annual variationkA=265cm

2

I _0 Depth, m c

I 100

I 150

(b) Phase lag with depth. The values of Xare the wavelengths of the thermal wave below 20 cm. The model used for the diurnal variation is from Apollo 17 data. (See the section entitled "Surface Temperatures Deduced From Thermocouple Measurements.") The annual curves are calculated from a Rima Hadley thermal properties model (ref. 9-14). FIGURE 9-3.-Peak-to-peak attenuation and phase lag as a function of depth.

9-8

APOLLO 17 PRELIMINARY SCIENCE REPORT These effects can be estimated by simplified analytical models and by laboratory experiments; both methods were used in the earlier analysis of the Apollo 15 results. However, for the Apollo 17 analysis and the refined Apollo 15 results presented in this report, a numerical model of the probe in a medium in which heat is flowing parallel to the probe axis has been used. The numerical model is more detailed and allows examination of certain combined effects that are difficult to estimate with analytical models. The numerical model computations show that the borestem and probe disturbances to the steadystate heat flow are small. In the extreme case, the temperature difference across a probe section is 7 percent lower than the temperature difference across the same vertical distance interval far from the borestem. The numerical model has been used to apply corrections to all probe observations. R ESU LTS Apollo 17 Subsurface Temperatures

nearly linear increase with depth below a few centimeters. Thus, the simple relationship of equation (9-7) would apply to a close approximation below these depths. The temperature at lunar noon varies throughout the year because of the varying distance of the Earth-Moon system from the Sun. The noon temperature increases approximately 6 K from aphelion to perihelion. The mean temperature (i.e., surface temperature averaged over a lunation) varies approximately 3 K throughout a year. Although the amplitude of the annual cycle is one-hundredth of the diurnal variation, the decay constant 5 is _ times smaller; consequently, annual variations penetrate deeper and induce significant heat flows to depths of a few meters and must be considered in the interpretation of the experimental results. The attenuation of amplitude and the increase in phase lag for the annual wave are shown in figure 9-3 as a function of depth, Annual wave effects shown in figure 9-3 are based on the conductivity profile at Rima Hadley. As shown in figure 9-3, temperature fluctuations attributable to the diurnal cycle become virtually undetectable at depths > 100 cm and would have had little effect on heat flow below this depth before the probe and borestem were emplaced. Once the borestem is emplanted in the regolith, the higher conductivity of the borestem and the radiative transfer inside the borestem will enhance the downward propagation of thermal waves. However, thermometers at 130 can below the surface do not detect any temperature variation during a lunation cycle. Corrections for the Shunting Effects of the Borestem and Probe The axial conductance of the epoxy borestem is considerably higher than that of a vertical column of lunar soil of equal cross section. This fact, combined with the finite length of the borestem, results in some shunting of the steady-state heat flow through the borestem to the surface. Certain short sections of the borestem, such as the bit and joints, are made of titanium or steel, and sizable disturbances occur near these parts. A second related effect results from the fact that the probes are radiatively coupled to the borestem walls and have a small axial conductance, Consequently, the probe bridges register slightly smaller temperature differences than those registered at points on the borestem next to sensors,

The HFE was turned on while probe 2 was being inserted into the borestem, and temperatures were recorded only minutes after drilling was completed. These temperatures ranged from 295 to 301 K. The early cooling histories of probe 1 indicate similar initial temperatures. After emplacement, the probes cool toward the undisturbed regolith temperatures. The temperature histories of all sensors deeper than 65 cm for the first 45 days are shown in figure 9-4. After 45 days, some sensors are continuing to cool; however, the expected future temperature decrease is probably less than the error of absolute temperature measurement. The equilibrium temperature differences and the absolute temperatures of each sensor are listed in table 9-1I. The correction for the steady-state disturbance of the heat flow by the borestem and probe system is applied to temperature data listed under the headings entitled "Corrected temperature difference" and "Corrected temperature." The appropriate corrections of the temperature difference attributable to the annual thermal wave during January 1973 (listed in the far right column) have not been applied because they are based on the conductivity profile at Rima Hadley. Note that the largest correction is approximately -4 percent.

the day and about half that value during the night. The values shown are calculated by subtracting the temperature at TC1 from that at TC4 and adding the result to the temperature at the top gradient sensor. Comparison of the temperatures measured by TCll and TC21 with those at the top gradient sensors shows relatively large errors in absolute temperature measurement (table 9-11I). The source of these errors has been traced to the copper/Kovar (Cu/Ko) junctions, in each thermocouple electronics circuit, that are mounted on circuit boards in the electronics housing. The errors are proportional to temperature differences between the Cu/Ko junctions. Thus, the errors in TC1 1 and TC21 are direct measures errors of this temperature difference and can be

larger errors at probe 2 junctions are caused by the gradients across the Cu/Ko junctions at night, and the used to distance between at all junctions. estimate errors the The in the larger greater probe 2 circuit. A preliminaryCu/Ko junctions electroanalysis of motive forces produced by Cu/Ko junctions that was used to to calculate the data the corrections in figure should be applied corrections

9-4. These

virtually

J 1200

measurements. The corrections have been applied to the data compiled in table 9-II. The uncertainty of erase the apparent corrections between nightas and day variation determining these is estimated -+ 0.4 K. Studies of the accuracies of the thermocouple measurements are continuing. The thermocouple temperatures given in table 9-II represent the averages of the values obtained during the time from lunar sunset of the first day to lunar sunset of the second day. The amplitude of the diurnal variation at 66 cm cannot be determined with the present accuracy of the data (+ 0.5 K). In figure 9-5, the equilibrium temperatures are plotted as a function of depth. Temperatures along the body of probe 1 show a steady decrease in gradient with depth. The gradient decreases from 0.016 K/cm in the depth range 130 to 177 cm to 0.012 K/cm in the range 185 to 233 cm. This decrease is principally due to a general increase in conductivity of the regolith over the interval of measurement. The thermocouple temperature indicares a gradient of 0.013 K/cm from 66 to 130 cm; however, the accuracy of this measurement is poor. At probe 2, the probe thermometers at a depth range of 131 to 234 cm indicate a rather uniform

300 afterprobe 600insertion,hr 900 Time (b) Probe 2 (TC24).

FIGURE 9-4.-ApoUo 17 temperature histories of all sensors 65 cm or deeper. The short pulses appearing on some of the sensor traces result from heater initiation for conductivity experiments. The numbers on each curve refer to the depths below the surface. The lowermost curves on each plot are TC4 thermocouple measurements. Some representative data points from the thermocouples are shown to indicate the scatter of these measurements, Temperatures shown are calculated by subtracting TC1 values from those of TC4 and adding them to the top gradient sensor temperature. The corrections given in table 9-III have not been added.

Temperature measurements of thermocouples TC14 and TC24 are also shown in figure 9-4. Some randomly sampled representative points are shown, and the solid curve is fitted visually to show the trend. The standard deviation of the points around

aThe accuracy of extrapolated absolute temperatures is ± 0.05 K for the platinum resistances. bThe correction for the annual wave to be applied to the tbermocouple is 0.04 K.

gradient of 0.0078 K/cm, whereas the gradient between 67 and 131 cm is 0.021 K/cm, a change by a factor of approximately 3. This large variation of gradient can be accounted for only partially by the variation of conductivity of the regolith immediately surrounding the borestem,

Apollo

15 Subsurface

Temperatures

Subsurface temperatures measured at Rima Hadley below the depth disturbed by diurnal variations were reported in reference 9-11 without correction for the annual wave. In addition, corrections for the bore-

stem and probe disturbance were derived from much simpler models than those discussed herein. Temperatures measured at longer times after probe insertion of equilibrium temperatures is possible. The temperatures and temperature differences at four sensors on probe 1 at Rima Hadley are presented in table 9-IV. More accurate corrections for the borestem disturbance and a correction for the annual wave effect have been applied. These measurements will be the basis for now available, are a slightly revisedand a more accurate determination heat flow value.

(b) Probe 2. FIGURE 9-5. Equilibrium temperatures, conductivities, and heat flows measured by the Apollo 17 probes. The open circles on the conductivity plot are calculated from cooldown circles assuming maximum drilling energy, and the solid curves are heater-activated experiment results. The solid line represents a layered model used for calculating heat flow. In the heat flow figure, the solid lines give heat flow over the three largest intervals. The geometry of the probe in the subsurface is shown at the far left. The large noise on the thermocouple data limits the accuracy of conductivities deduced from the cooling history. Deductions of the conductivity at depths from 3 to 15 cm below the surface, which will be discussed later in this section, give values of approximately 1.2 X 10 -4 W/cm-K. Based on these results at shallow depths, we estimate the conductivity lies in the range 1.0 × 10 -4 to 1.6 X 10 4

energy associated different initial These cases have section on theory.

with drilling, two cases assuming conditions have been examined, been described in the preceding Results derived assuming initial

borestem and contact zone temperatures to be equal to the initial probe sensor temperature are listed in table 9-V under the heading entitled "Conductivity with drill heating effects." Conductivity estimates derived assuming that only the borestem and probe were initially at elevated temperatures are listed under the heading entitled "Conductivity without drill heating effects." The two cases are considered to be bracketing assumptions of the actual initial conditions. Cooldown conductivity estimates were made for each of the eight sensors along each probe, Additionally, cooldown analyses were performed assuming drill heating effects for the thermocouples located 65 cm above each probe,

cannot be neglected if reliable conductivity information is to be extracted from When the next section, it is evident the cooldown data. effects that drill heating substantial drill heating effects are included in the cooldown analyses, conductivity determinations and variations with depth agree well with the heateractivated conductivity experiment results. The cooldown conductivity estimates are particularly valuable in interpolating between the more accurate heateractivated conductivity determinations.

HI1 H12 H13

n14

Heater-Activated Conductivity Experiments
Conductivity experiments heater locations have been shows the sensor temperature at each of the eight performed. Figure 9-6 rise history and thee-

H21 H22 H23

retical curves for one such experiment. The conductivities k m and contact conductances H_ are given in table 9-VI. These results and the cooldown estimates with drill heating effects are shown clear that the conductivity does simple way with depth. in figure 9-5. It is not vary in any

H24

HEAT FLOW EXPERIMENT

9-13

,H2 = 1.5 x 10 -4 Wlcm2-K

0.4

/

.3

_ .=_= .02 km=2.4x 10 W/cm-K .4 /e •

e .2
_
.1

_...._P-0 20 L 24

km =2.7x 10-4 W/cm-K t 28 Time, hr
I I

_k
E

_-

t 32

J 36

ltO

20 Time afterturn-on, hr

30

FIGURE 9-6.-Temperature rise during a conductivity experiment (dots) is compared with a theoretical curve derived from a model with km = 2.7 X 10-* W/cm-K and H2 = 1.5 X 10 -4 W/cmZ-K. In the inset, the temperature rise for times > 1000 min is shown on an expanded scale plotted against the logarithm of time. The ol:,served data are compared with two bracketing theoretical curves. The reduced conductivity is 2.64 W/cm-K. A rough correlation exists between the drill penetration rate during borestem drilling and the measured conductivity. The more resistant layers where the drill penetrated slowly correspond to depths where higher conductivity is observed. The more resistant layers likely correspond to more compacted regolith materials or possibly to a higher concentration of centimeter-size rock fragments, Either of these phenomena can increase the bulk conductivity. The relatively high conductivity measured at 130 cm on probe 1 lies within a zone from 80 to 130 cm where penetration was slow. Directly below this layer, drilling rates were relatively high and the conductivity values are correspondingly lower, These correlations are used to interpolate values between discrete measures. In figure 9-5, the solid line that passes through the heater-activated conductivity values represents a layered model of conductivity in the regolith based partly on penetration rates and partly on cooldown estimates. At probe 2, some of the drilling operation was not visually monitored so that correlations with conductivity cannot be made during the unmonitored period, winch includes approximately half the depth range where probe 2 is emplaced. One interesting feature of these conductivity results is a rather large difference between the conductivity prof'fles at probe 1 and probe 2. It is possible that layers, as defined by conductivity, have some dip relative to the surface. For example, the high conductivity layer at 100 cm at probe 1 could correspond to the high conductivity layer between 170 and 230 cm at probe 2. The contact conductance //2 arises from low conductivity material lying in a disturbed zone just outside the borestem. We estimate this zone to be 2.2 rnm thick. The conductivity k c of material in the contact zone is given by ( k e = tt 2\b t,r,_ [b + Ap'_ + -_)ln_=-"ff --] (9-9)

(See fig. 9-2 for definition of parameters in this equation.) As an example, for H 2 = 1.4 X 10 -4 W/cm%K, kc = 3.0 X 10 -s W/cm-K. This value of conductivity is approximately a factor of 6 less than that of the surrounding regolith.

The magnitude of the vertical component of heat flow in the regolith can be calculated from the temperature depth interval zl to z2 and conductivity profiles Over each &T
Zl_Z 2

in figure

9-5.

(9-10)

[

ave z 2 - z 1

where ATza-z2 is the corrected temperature difference listed in tables 9-II and 9-IV and kave is the average conductivity in the depth interval zl - z2 Gradients, average conductivities, and heat flows

calculated from the Apollo 15 and Apollo I7 results are presented in table 9-VII. The heat flow data over calculated from the layered models in figure 9-5. the entire depth range of temperature measurement

TABLE

9-VIl.-Heat

Flow Data Heat flow, W X 10 6

aThe estimated error of conductivity measurement is -+15 percent, bEstimated error is +-20 percent. In the theoretical model the thickness of the contact zone is 2 ram. eIt is probable that a section of broken borestem lies just outside this location so that the uncertainty of this measurement is very large.

Six conductivity experiments using a heater power of 0.002 W were performed on the Apollo 15 probes. The analyses of three of these measurements were not described in reference 9-11 because it was very difficult to separate changes attributable to heater turn-on from large diurnal variations in temperature. Snbsequently, two of the measurements have been repeated at times in the lunation when the rate of temperature change at the heater location was minimal. In addition, the diurnal temperature variation from preceding and succeeding lunations is available to help interpolate trends during the time that the heater is on. Lastly, some refinements have been made in the finite difference models of the conduc-

HEAT FLOW EXPERIMENT are presented on the bottom lines of table 9-VII for Apollo 17 probes 1 and 2. At probe 1, the most representative value of heat flow (2.8 X 10-6 W/cm 2) is thought to be that determined by the probe data over the interval 130 to 233 cm. At probe 2, the measurement is possibly disturbed, as will be discussed in the next section, and the most representative value (2.5 × 10 -6 W/cm 2) is that calculated using data between 67 and 234 cm. The heat flow calculated over the interval 91 to 138 cm is believed to be the best value from the Apollo 15 measurements. At the Apollo 17 probe 1 site, the [teat flow is quite uniform over the entire depth range. The variation falls well within the estimated error of measurement. Probe 2 results show a uniform heat flow along the length of the probe, but heat flow between 67 and 131 cm is 70 percent greater. The large change in gradient is partly compensated for by an increase in conductivity with depth. The overall heat flow of 2.5 X 10 -.6 W/cm 2 is in fair agreement with the probe 1 value of 2.8 × 10 -6 W/cm 2 . DISCUSSION OF HEAT FLOW RESULTS

9-15

The Probe 2 Measurements The change in heat flow at probe 2 by a factor slightly less than 2 over the depth range of 67 to 234 cm is most reasonably explained by refraction of heat flow in the vicinity of a large buried boulder. A rdatively large number of rocks are strewn over the ALSEP area. Lunar basalts have conductivities of approximately 1.2 X 10 -2 to 1.8 X 10-2 W/cm-K at 250 K (ref. 9-15). These values are 60 to 90 times the conductivity of the fine-grained regnlith material. Thus, large blocks of solid rock in the subsurface can result in significant shunting of heat flow. To illustrate the shunting effect, the distortion of heat flow lines and isotherms around and through a square of material having 60 times the conductivity of a surrounding infinite medit, m is shown in figure 9-7. The model is two-dimensional and symmetric at the left margin of the figure. One significant feature of the model is that very little effect is evidenced at distances greater than one-half of the width of the rock. Thus, heat flow measurements wouldhave to be made quite close to a rock (less than one-fourth of the width) to detect a disturbance as large as that at probe 2. However, probe 2 must be more than 5 cm

FIGURE 9-7.-The effect of a square of material on vertical heat flow (shaded area) which has a conductivity 60 times that of the surrounding material, shown by the distortion of isotherms and flow lines. These results are based on a finite difference model computation.

from a rock in order for the rock not to have a detectable effect on the heater-activated conductivity experiments. If probe 2 were located relative to a large subsurface boulder in a zone defined by the dashed rectangle ha figure 9-7, a temperature profile similar to that observed would result. Other features such as

9-18

APOLLO 17 PRELIMINARY SCIENCE REPORT However, loss tangent measurements yield values in the range 0.0004 to 0.01 and are frequency dependent (refs. 9-20 and 9-22). Additional electrical property measurements and refined analysis of the existing data on regolith samples must be made before the thermal gradient measured in situ can be supported on a moonwide gradient observations. basis by the spectral

tion coefficient for the lunar-surface/space interface. For the very low electrical conductivities found in the lunar regolith, the electromagnetic penetration depth £e(X) may be written for the centimeter wave spectral region as J_e(X) = X/(2_r¢_-_tan A) (9-12)

where e is the dielectric constant and tan A is the loss tangent at centimeter wavelengths. The average temperature gradient of 0.017 K/m measured in situ at the Apollo 15 and 17 sites would produce the observed spectral gradient if_/etan ,5 _ 0.003, assuming R = 0.05. The feasibility of such a value for _ tan _ is supported by direct surface observations in the 0.4- to 3-cm wavelength range (ref. 9-19). Direct measurements of returned Apollo samples over a wide range of frequencies indicate a dielectric constant for the regolith material in the range 2.2 to 3.2 that is nearly frequency independent, The Representativeness of the Two Heat Flow Measurements The regional geological settings of Rima Hadley and Taurus-IJttrow are quite similar. Both are located on lava-flooded emhayments at the edge of mascon basins. If the heat flow is influenced by structural or compositional anomalies unique to this type of region, the anomalies would affect both measurements. To that extent, they would not be representatire of global flux from tire Moon. However, the

FIG. 9-8. Photograph of probe 2 borestem protruding from the lunar surface. The heat flow experiment housing is in the background. The thermocouple is in the black portion of cable approximately i0 cm from the top of the stem (AS17-134-20492).

HEAT FLOW EXPERIMENT possible compatibility of the results with the microwave emission spectral gradient between 5- and 20-cm wavelengths lends support to the possibility that local anomalies at the two sites are not large. Despite the reservations in the previous paragraphs, the existing data concerning heal: flow from the lunar interior indicate that a significant area of the Moon is characterized by a flux of between 2.5 and 3.0 pW/cm 2 . Numerous thermal history calculations have shown that the contribution of initial heat (e.g., that gained during accretion) to the present surface flux is relatively small (refs. 9-11 and 9-23) even if the Moon were molten throughout initially. Some scientists have suggested that, at the present time, the Moon is thermally at steady state (e.g., ref. 9-24). In either case, it follows that a predominant part of the surface flux (2.0 to 3.0 #W/cm 2) must result from radioactive isotopes in the Moon. The geochemical data are convincing that most of these isotopes are concentrated in the outer layers of the Moon. In addition, the abundances indicated by the heat flow values would require the heat sources to be located near the surface to prevent melting in the outer several hundred kilometers. The radiogenic heat production per cubic centimeter of rock can be expressed in te_ms of the abundance of uranium, because the ratios of the other important long-lived, heat-generating isotopes (4°K and 232Th) to uranium are well established and quite uniform in the lunar samples. The heat prodnction per unit volume at the present time in W/cm 3 is approximately 0.71 times the uranium abundance in parts per million (e.g., refs. 9-23 and %25). If most of the uranium is concentrated within 300 km of the surface so that it contributed to the present flux, then the total lunar uranium abundance required to contribute 2.0 to 3.0 /tW/cm 2 to the heat flow is approximately 0.05 to 0.075 ppm. These abundances are much greater than chondrites and significantly higher than estimates of the Earth abundance of approximately 0.03 ppm(ref. 9-4).

SURFACE TEMPERATURES DEDUCED FROM THERMOCOUPLE M EASU R EM ENTS At each of the two heat flow holes, one of the thermocouples is embedded in a section of the cable that is approximately 15 cm from the top of the borestem and suspended above the lunar surface as

The first term on the right side of equation (9-13) iepresents flux into the cable element from the lunar surface; the second term represents direct flux from the Sun; the third term represents solar energy ieflected diffusely from the lunar surface and impinging on the cable. The radiative properties of the cable ec, acir, and %s were determined by laboratory measurement before the Apollo 17 mission. The cable orientations tbr both probe locations were determined from ALSEP photographs. Solving equation (9-13) for the surface brightness temperature yields

9-22

APOLLO 17 PRELIMINARY SCIENCE REPORT much as a factor of 2 in conductivity determinations for depths below 2 cm (curve 17a, fig. 9-10 inset). CONCLUSIONS During the Apollo missions, two heat flow measurements were successfully made on the lunar surface. Both measurement sites are ha similar regional settings in the northeast quadrant of the Moon. The Taurus-Littrow and Pdma Hadley sites are located in embayments in the mountainous rims of the Imbrium and Serenitatis mascon basins that have been flooded by mare-type basalts. Surface brightness temperatures were calculated from the temperature of thermocouples suspended several centimeters above the lunar surface. The mean surface temperature at Rima Hadley throughout a lunation cycle is 207 K. The mean temperature increases with depth very rapidly in tire upper few centimeters and is approximately 252 K at a depth of 90 cm. The main reason for this increase of 45 K is the predominant role of radiative heat transfer in the loosely packed upper layer. During the lunar night, the surface temperature at Rima Hadley falls to 93 K. From the cooldown history after sunset, we have deduced that the upper 2 cm of the regolith is characterized by a conductivity of 1.5 X 10 -s W/cm-K. Below this depth, the conductivity increases rapidly and probably in a continuous manner until it reaches values of approximately 1.5 × 10 -4 W/cm-K at depths where the probes are emplaced. At Taurus-Littrow, the mean surface temperature is 216 K and, as in the case of Rima Hadley, increases a few tens of degrees in the upper 2 cm so that, at a depth of 67 cm, a mean temperature of 254 K is measured. The minimum temperature just before lunar dawn is 103 K, 10 K higher than that at Rima Hadley. This higher temperature is primarily attributable to the existence of a relatively high conductivity layer at a depth 2 cm below the surface. From the point of view of thermal properties, the regolith at Taurus-Littrow can be described as two layers: an upper 2-cm, loosely packed layer of very low conductivity (1.5 X 10 -s W/cm-K) in which heat transfer by radiation predominates and a lower layer with much higher conductivity (> 1.2 × 10 -4 W/cm-K) and higher density (1.8 to 2.0 g/cm 3). Subsurface temperature and conductivity measurements at depths below 90 cm, where the large diurnal variations are negligibly small, indicate a steady-state

core penetration rates and surface disturbance caused by crew activity reported by J. Mitchell (personal communication, 1972) of tire Apollo 15 soil mechanics team. The density profile for the Apollo 17 site was determined from preliminary examination of returned core tube samples (D. Carrier, personal communication, 1973). In both the Apollo 15 and 17 models, the heat capacity as a function of temperature was taken from Robie et al. data (ref. 9-29) on returned Apollo 11 samples. In both models, a low conductivity layer approximately 2 cm thick is required to fit the steep drop in surface temperature immediately after sunset. The Apollo 15 model then requires a steep, but not discontinuous, rise in conductivity with depth down to 5 cm to produce the increased flattening of the cooldown curve through the lunar night. The Apollo 17 model, however, requires a very sharp rise in conductivity at a depth of approximately 2 cm to produce the abrupt flattening of the cooldown curve at a phase angle of approximately 190 °. The subsequent increase in conductivity with depth is slight enough so that the Apollo 17 model may be considered essentially a two-layer model. The large jump in conductivity at 2 cm is also supported by the preliminary density prof'de, which indicates a fairly high density quite close to the surface. The Apollo 15 density profile, however, supports the possibility that a substantial conductivity gradient exists over the upper 30 cm of the regolith, The most critical surface temperature data required for the purpose of determining thermal regolith profiles are those obtained during the 10 to 30 hr immediately after sunset. Surface temperature data during this period have been the most difficult to obtain from remote infrared brightness scans. The level and steepness of the cooldown data immediately after sunset are controlled almost entirely by the thermal properties of the upper 2 cm. If the very early nighttime data are not sufficiently accurate to constrain the thermal properties of the upper 2 to 3 cm of the dust layer within -+30 percent, then subsequent attempts to determine deeper conductivity values unambiguously from the flattened part of the cooldown curve will not be possible. For example, the broken-line curve of figure 9-10 fits the nighttime data after 192 ° phase angle well within the error bands of the data. However, discrepancies in the early postsunset fit produced by different conductivities within the upper 2 cm lead to discrepancies as

HEAT FLOW EXPERIMENT heat flow through the surface at Rima Hadley of 3.1 × 10 -6 W/cm 2 and at Taurus-Littrow of 2.8 × 10 --6 W/cm 2 with an estimated error of -+ 20 percent, These fluxes are deduced from average temperature gradients in the regolith between 1.3 and 1.7 K/m and an average conductivity in the range of 1.7 X 10 -4 to 2.0 X 10 -4 W/cm-K. Conductivity generally increases with depth in the regolith although some layering, with high conductivity materials overlying lower conductivity materials, is found at both sites (table 9-VI). A conductivity value of almost 3 X 10 -4 W/cm-K was measured at the bottom of probe 1 at the Apollo 17 site. Thermal gradients decrease with depth, in some cases, in response to the increase in conductivity. At Taurus-tittrow probe site 2, a large decrease in gradient with depth is possibly attributable to a large subsurface boulder in close proximity to the probe, The heat flows at both sites are affected to some extent by local topography. Preliminary estimates indicate that a correction of -15 to -25 percent may be applicable to the Taurus-Littrow values because of the adjacent massifs. However, a more refined analysis is required. The heat flow measured at the two sites is

9-23

more refined microwave observations of the Moon, especially narrower beamed measurements over discrete portions of the lunar disk, would be valuable in determining possible variations of heat flow over the lunar surface.

approximately one-half the average heat flow of the Earth (6.3 X 10 -6 W/cm2). If these two values are representative of heat flow from the Moon as a whole, then a heat flow of one-half that of the Earth requires a heat production per unit mass for the lunar interior of more than twice that of the Earth. This statement assumes both planetary bodies are near

steady state so that total surface heat loss is nearly equal to the present interior heat production, Because the long-lived radioisotopes of 4°K, 23su, 238U, and 232Th are the principal source of heat in

the Earth and Moon, the heat flow results imply a twofold to threefold enrichment of uranium in the Moon relative to that in the Earth. Lunar samples show that the abundance of potassium relative to uranium is one-third to one-fourth that of the Earth SO that, in the Moon, uranium is the main contributor to internal heating. At present, these isotopes must be concentrated in the outer 100 to 200 km of the Moon to avoid extensive melting at shallow depth. Reinterpretation of Earth-based measurements of microwave brightness temperatures using the new data on regolith thermal and electrical properties will be important in determining the representativeness of the in situ lunar heat flow measurements. Additional,

The successful installation of a geophysical station at the Taurus-Littrow landing site of the Apollo 17 mission marked the culmination of an exciting period of manned lunar exploration and vastly improved current knowledge of the lunar interior. Before the Apollo 17 mission, there was a gap in our knowledge concerning the upper 10 km of the lunar crust because of the large hiatus in pertinent traveltime data between the coverage provided by the previous active seismic experiments on Apollo 14 and 16 and that of the earlier lunar module (LM) and SIVB impacts. In particular, it was not possible to resolve whether the seismic velocity increased smoothly or stepwise in the upper 5 km of the Moon. The purpose of the Apollo 17 lunar seismic profiling experiment (LSPE) was to record the vibrations of the lunar surface as induced by explosive charges, by the thrust of the LM ascent engine, and by the crash of the LM ascent stage. Analyses of these seismic data were planned to determine the internal characteristics of the lunar crust to a depth of several kilometers. The traveltimes of seismic waves are inverted to determine the seismic velocity structure with depth and to provide the direct means of probing the lunar interior. A secondary objective of the LSPE was to monitor lunar seismic activity during periodic listening intervals. Strong seismic signals were recorded from the detonation of eight explosive charges that were armed and placed on the lunar surface by the crewmen at various points along the traverses. Recording of these seismic signals generated traveltime data to adistance of 2.7 kin. One of the more significant events of the Apollo 17 mission was the recording of the seismic signals from the LM ascent stage, which struck the lunar astanford University. bThe University of Texas at Galveston. "_'Principallnvestigator.

surface 8.7 km southwest of the landing site. The characteristic reverberation from this impact spread outward and was first detected at the Apollo 17 station approximately 6 sec after impact. The seismic signals received from this impact provided a valuable travelfime datum for determining the variation of seismic velocity with depth in approximately the upper 5 km of the Moon. The most significant discovery resulting from the analysis of the data recorded by the LSPE is that the seismic velocity increases in a marked stepwise manner beneath the Apollo 17 landing site (fig. 10-1). A surface layer with a seismic velocity of 250 m/see and a thickness of 248 m overlies a layer with a seismic velocity of 1200 m/see and a thickness of 927 _a, with a sharp increase to approximately 4000 ra/sec at the base of the lower layer. The seismic velocities for the upper layers are compatible with those for basaltic lava flows, indicating a total t_hickness of approximately 1200 m for the infflling mare basalts at Taurus-Littrow. Major episodes of deposition or evolution are implied by the observed abrupt changes in seismic velocity.

INSTRUMENT DESCRIPTION P E R F O R MA NC E

AND

The LSPE consists of a geophone array, eight explosive packages, and electronics within the Apollo hmar surface experiments package (ALSEP) central station. Four identical geophones are used in a triangular array; the geophones are miniature seismometers of the moving coil-magnet type. The coil is the inertial mass suspended by springs in the magnetic field. Above the natural resonant frequency of the geophones (7.5 Hz), the output is proportional to ground velocity. The LSPE geophone array was deployed without difficulty in the nominal eonfiguration at the Apollo 17 site approximately 148 m 10-1

west-northwest of the LM (fig. 10-2). Figure 10-3 is a photographic panorama from geophone 2 to the LM as viewed from geophone 3. A four-channel amplifier and a logarithmic cornpressor condition the geophone signals before conversion into a digital format for telemetering to Earth. Because the LSPE signal levels are distributed throughout the dynamic range of the system, loga-

rithmic compression is used. This compression gives signal resolution as some constant fraction of signal amplitude. The logarithmic compressor used in the LSPE has tile transfer function + (i0-i)

Vout = +-Min lib' Vin

e

where V is voltage, the constant M determines tile slope of the transfer function, and b' is specified by the dc offset of the compressor output and the system noise level. The values of M and b' a/e determined by calibration of the system to provide at least 6-percent accuracy of the data referenced to file level of the input signal. The properties of the LSPE system are listed in tables 10-I and 10-II, and the nominal frequency response is shown in figure 10-4. The output of the logarithmic compressor is referenced to 2.5 V dc. The analog output of the logarithmic compressor is converted to a 7-bit binary element in the LSPE control electronics by an analog-to-digital converter

G = geophone Sync = synchronous FIGURE 10-5.-The LSPE data format. Each data frame consists of three subframes of twenty 30-bit words each. Geophone data words are normally ? bits long except for those in word 1, which are 5-bit samples. and one 5-bit seismic data sample from each of the four seismic data channels. Words 2 to 20 of each subframe are 7-bit samples from each of the four seismic data channels. Engineering data are interleaved and subcommutated, using the remaining 2 bits to form 30-bit words, In words 2 to 19, geophone samples are sampled on the bit preceding the word on which they are read out; the most significant bit is read out first. In the first word of each subframe, the timing of the data sampling is the same as that in words 2 to 19 except that the samples are stored and read out in the last 20 bits with one 5-bit word/channel. The time of the RF fire pulses must be accurately known. When the LSPE is commanded to the fire

pulses "on" mode, a fire pulse set is transmitted once every 29.55 sec and is flagged in word 3 of subframe 1. This occurs once every 58 frames. A command system provides for 11 commands associated with the LSPE. Two commands turn the LSPE on and off; two commands control the bit rate; and two commands control down-link formatting. In addition, commands are used to control amplifier gain status, transmission of the geophones. of fire pulses, and calibration

Explosive Package Description and Performance
An LSPE explosive package is shown 10-6. The eight explosive packages are in figure identical

LUNAR

SEISMIC PROFILING

EXPERIMENT

10-5

except for the amount of high explosive and the preset runout time of the mechanical timers. An explosive package is activated by removing three pull pins (fig. 10-6). Removal of the first pull pin activates the SAFE/ARM slide timer, which is preset at 89.75, 90.75, 91.75, or 92.75 hr. Removal of the second pull pin releases the SAFE/ARM slid(.= from its constrained SAFE position. Removal of the third pull pin removes a constraint on the firing pin and activates the thermal battery timer. The LSPE transmitter, which is located within the ALSEP central station, transmits a repetitive pulsed carrier signal. A series of three pulses properly spaced in time is required to signal processor within detonate the explosives activated by the timer, This 2 rain provides a ensure that elicit a FIRE signal from the the explosive package and to train. The thermal battery, has a minimum life of 2 min. time window long enough to while

the explosive package is energized electrically. Because the seismic data subsequently collected must be _Lccurately referenced to the instant of detonation, it ks necessary to establish which specific set of pulses is effective. This is done by comparing known times of pulse-set transmission with the time of arrival at the geophones of the initial seismic data. Pulse sets are spaced at 29.55-sec intervals to make such identification possible without ambiguity. No difficulty was experienced in the deployment of the explosive packages during the periods of extravehicular activity (EVA) (fig. 10-7). The 454-g explosive package (EP-6) was deployed at station 1, and the 227-g explosive package (EP-7) was positioned on the return to the LM from station _1. Explosive packages 4, 1, and 8 were armed and placed on the lunar surface during the second EVA. During the third EVA, explosive packages 3, 5, and 2 were deployed. It was necessary to place the 1361-g

explosive package (EP-5) at station 9 when it became apparent that insufficient time remained for a visit to the crater Sherlock. All the explosive packages were successfully detonated (table t 0-III), and the detonation of EP-7 was visible from the television camera on the lunar roving vehicle (LRV). Figure 10-8 is a photograph showing EP-8 on the lunar surface approximately 296 m west of the LM. DESCRIPTION OF RECORDED SEISMIC SIGNALS

The Apollo 17 LSPE was planned to contribute to the understanding of the shallow lunar structure in two major ways: (i) by providing traveltimes of the seismic signals from explosive packages, which were to be detonated on the lunar surface at distances ranging from 100 to 2700 m, to the LSPE geophone array and (2) by impacting the Apollo 17 LM at a nominal distance of 10 km to provide traveltime data for deciphering the variation of seismic velocity with depth in the upper 5 km of the Moon. In addition, monitoring of the seismic signals generated by the LM ascent en_e at lunar lift-off provided useful data. Lunar Module Ascent The LSPE was commanded on at 22:24:00 G.m.t. on December 14, 1972, to record the impulse produced by the thrust of the LM ascent engine. The effective zero time for the seismic impulse from the LM ascent-engine ignition was determined from NASA postflight analyses, which gave engine buildup pressure data at 5.msec intervals for the LM lift-off. The assigned ignition time of 22:54:38.424 G.m.t. corresponds to the time when the LM ascent engine achieved 20 percent of its maximum propulsion pressure. Clear seismic signals were recorded by the LSPE geophone array at distances of 148,244, 190, and 187 m (fig. 10-9). Interpretation of the traveltime data is presented in the subsection entitled "Shallow Lunar Structure."

FIGURE 10-8.-Photograph of EP-8on the lunar surface 296 m west of the LM (AS17-145-22184).

impact. The impact occurred at latitude 19.91 ° N, longitude 30.51 ° E, 8.7 km southwest of the Apollo 17 landing site. Other pertinent parameters for the LM impact are given in table 10-IV. A portion of the seismic signal from the Apollo 17 LM impact is shown in figure 10-10 in a compressed time scale. The impact signal is similar in character to previous impact signals; that is, these signals have an emergent beginning and a long duration. The initial portion of the impact signal on an expanded time

aRange time is the time the signal of the ewmt was observed on Earth. scale is shown in figure 10-11. The arrival time of the first compressional wave (P-wave) is rrmrked at 06:50:25.35 G.m.t., giving a traveltime of 5.75 sec. The amplitude of the impact signal is of interest when previous previous compared with the P-wave amplitudes for LM and SIVB impact signals. Comparison of LM impact and SIVB impact signal ampli-

Beginsat 06:.50:14.027 G.m.t. FIGURE 10-10.-Compressed time-scale record of the seismic

signal received from the Apollo 17 LM impact (Dec. 15). Arrows point to measured first and second seismic arrivals. the Apollo 17 LM ascent stage striking the side of the mountainous South Massif rather than grazing the lunar surface. In other words, if the predicted amplitude of 26 nm is multiplied by the factor 17.4, the resulting figure is 452 nm, which agrees well with the observed amplitude of 400 nm. The LM impact traveltime data are discussed in the subsection entitled "Shallow Lunar Structure."

tudes demonstrated that the LM impact data had to be adjusted upward by a factor of 17.4 to allow for the lower kinetic energy and a shallower angle of impact. Extrapolating the earlier LM impact data to a distance of 8.7 km leads to a predicted peak-to-peak mnplitude of 26 nm. The Apollo 17 LM impact signal is centered at 4 Hz and has a measured peak-to-peak amplitude of 400 nm. This amplitude was caused by

Geophone 4 Geophone 3 FIGURE 10-11.-Expanded time-scale record of the seismic signalfrom the Apollo 17 LMimpact. !Geophone 4 Analyses of previous lunar seismic impact signals (ref. 10-1) have demonstrated that many of their characteristics (signal rise time, duration of signal, and lack of coherence between horizontal and vertical components of motion) can be explained by wave scattering. Seismic energy is considered to spread with a diffusivity _ proportional to the product of the average seismic velocity and the mean distance between scattering centers; that is, the larger the value of diffusivity, the smaller the amount of scattering. For a surface impact, the theory predicts (ref. 10-1) that the signal rise time (the time from signal onset to its maximum value) is given by R2/_ where R is the range. The Apollo 17 LM impact seismic signal rise time of 56 sec leads to a diffusivity of 1.35 km2/sec, which is significantly larger than the value of 0.033 krn2/sec inferred at the Apollo 16 site (ref. 10-2) from analysis of the seismic signals generated by the LRV at distances of approximately 4 km. The implication is that the Apollo 17 landing area is more homogeneous, for the dimensions of the seismic waves considered (approximately 25 m), than either the Apollo 15 or 16 landing areas. Such a difference in near-surface properties of these landing sites may be attributable to differing ages of the different areas and to the effects of differing amounts of comminution and gardening by meteoroid impacts, Begins at23:16:23.027 G.m.t. FIGURE t0-12.-Seismic signals produced by detonation of EP-5 on the lunar surface (Dec. 17). Arrows point to onset of seismicarrival.

Transmissions of the fire pulses at 29.55-sec intervals from the LSPE antenna (fig. 10-2) were observable as crosstalk on the individual geophone data channels and produced convenient, accurate references for selecting the detonation time of the individual explosive packages. The locations of the explosive packages with respect to the LSPE geophone array were taken from preliminary postmission analyses (refs. 10-3 and 10-4). Adjustments in the absolute distances of the explosive packages will undoubtedly be necessary when subsequent analyses of the appropriate Apollo 17 lunar surface photographs are completed. However, it is not anticipated that any revisions in the distances will have a major effect on the traveltime data discussed in the following subsection. SHALLOW LUNAR STRUCTU RE

Explosive

Packages

The traveltime/distance data obtained from the detonation of the eight explosive packages are shown in figure 10-13. Two sets of seismic wave first arrivals were observed traveling at velocities of 250 and 1200 m/see. The shortest explosive-charge-to-geophone distance was approximately 100 m. If a seismic velocity of 100 m/see is assumed for the regolith at the Apollo 17 site, a regollth as thick as 25 m would not have been detected. The depth of penetration of seismic waves is nominally one-fourth the explosive-charge-

All eight of the explosive packages placed on the lunar surface were successfully detonated. The seismic data recorded for EP-5, which was detonated at station 9, are shown in figure 10-12. The arrows point to the measured onset of the first seismic arrival,

to-receiver distance. However, it is probable that the regolith is significantly thinner than 25 m, inasmuch as the 250-m/see velocity curve extrapolates to a zero intercept time. The faster seismic arrival with a velocity of 1200 m/see was observed beginning at a distance of 612 m, E I00

Z = At

VoVl 2 _ Vo2 Z = 128 m Camelot

/EP-1

LSPE array; ,/

V = 250 m/see 0 2500_J 3000

indicating that the thickness of the 250-m/see material was 248 m. Considering uncertainties in the charge distances and in the inferred seismic velocities, the depth estimates are considered cent. The 1200-m/see velocity accurate to 10 perwas observed to a

distance of approximately 2.5 km. At this distance, the observed traveltimes for EP-1 were offset by approximately 0.5 sec with respect to the 1200-m/see line. Examination of the path between EP-] and the LSPE geophone array revealed that the seismic path was affected by the presence of the 600-m-diameter crater Camelot. The observed time delay on the seismic path can be explained by postulating that low-velocity material extends to a greater depth beneath the crater Camelot than along the remainder of the traveltime path. A simple model approximation for Camelot Crater that explains the observed traveltime delay is shown in figure 10-14. The traveltime data from the LSPE explosive charges can be combined with the observed traveltime for the LM impact to provide information about the

FIGURE 10-14.-Model approximation for seismic ray path from EP-1 to LSPE array that crosses Camelot Crater. Observed time delay is produced by presence of lowvelocity material (of tttickaess Z) beneath crater. seismic velocity to a depth of several kilometers. Traveltime data from the seismic signals produced by the LM impact and the explosive charges are shown in figure 10-15. A line with an apparent velocity of 4 kin/see can be fitted through the LM impact data point to intersect close to the corrected traveltime data point for EP-1. Because of obvious uncertainties in allowing for the time delay through the crater Camelot, there is no a priori reason to force a specific apparent-velocity line through the EP-1 data point. The first-order conclusion is thathigh-velocity material (_4 km/sec) must lie beneath the 1200-m/see material.

Distance,km FIGURE 10-15.-Seismic traveltimes from LM impact and LSPE explosive charges. Traveltime for EP-I has been corrected for Camelot Crater delay, and LM impact traveltime has been corrected for 1.2-kin elevation difference between the impact point and the LSPE array. These corrections shift the position of the 4-km/sec apparent velocity slightly downward as shown.

1.06

20

25

Inasmuch as the LM impacted at an elevation of 1.2 km (fig. 10-1) above the vaUey floor at the ApoUo 17 landing site, the LM impact traveltime can be adjusted to the same reference elevation as the LSPE geophone array. The 1.2-kin difference in elevation contributes an additional delay time equal to the ratio of the elevation difference to the seismic velocity of the material traversed multiplied by the cosine of the angle of incidence at which the particular seismic arrival under consideration departed the source (impact point). Inserting the appropriate values in this case leads to a time correction of 0.18 sec. This correction will shift the position of the 4-krn/sec apparent-velocity line downward as shown in figure 10-15 such that its zero distance time intercept is decreased. The end result is a decrease in the derived thickness of the 1200-m/sec material from 1020 to 927 m. It is possible that a dipping interface exists beneath the 1200-m/sec material that might result in a high apparent velocity, or that the particular seismic ray passed through a high-velocity heterogeneity somewhere along its path. Some of the uncertainty may be resolved by subsequent digital velocity filtering (beam steering) of the LM impact signal on the LSPE array,

1"6x I08

300

1

2

3 4 5 Velocity, m/sec k

6--7

FIGURE 10-16.-Inferred compressional-wave velocity ptofdes for the Moon and velocities of lunar and terrestrial rocks measured in the laboratory as a function of pressure. Lunar rocks are identified by sample number. Lunar models 1 and 2 are based on results available through Apollo 16. Apollo 17 results reveal a marked stepwise increase hi seismic velocity in the upper 2 km of the Moon. Before the Apollo 17 mission, the best estimates of the seismic velocity variation in the upper 20 km of the Moon were as depicted by lunar model 1 or 2 in figure 10-16. The seismic velocity was known to increase very rapidly from values of 100 to 300 m/sec in approximately the upper 100 m to a value of km/sec at a depth of 5 km. Even though the seismic velocity variation was depicted as a smooth increase with depth, it was surmised (ref. 10-5) that such a rapid increase of velocity (_2 km/sec/km) could not be explained solely by the pressure effect on dry rocks with macrocracks and microcracks nor by the self-compression of any rock powder. Laboratory velocity measurements on returned lunar soils (refs. 10-6 to 10-10) and recent measure-

LUNAR SEISMIC PROFILING EXPERIMENT ments under hydrostatic pressure conditions on terrestrial sands and basaltic ash have indicated velocitydepth gradients of 0.4 to 0.8 km/sec/km, but such gradients occur only to pressures of _50 × l0 s N/m _ (a lunar depth of _1 km). The measurements on unconsolidated sands and rock powders also have demonstrated that no unique relation exists between seismic velocity and porosity in granular material. An examination of these experimental d_ta led to the inference that compositional or textural changes must be important in the upper 5 km of the Moon (ref. 10-5). The LSPE results have shown that, at least beneath the Taurus-Littrow site, the seismic velocity increases in a stepwise manner in the upper several kilometers, It is of interest to examine the in situ velocity information with reference to the surface geological investigations at the Apollo 17 site, the laboratory velocity measurements from returned lunar samples, and the seismic velocity measurements on terrestrial lunar analogs, Premission analyses indicated that much of the Apollo 17 landing site area is covered by a dark mantling material, possibly volcanic ash (ref. 10-11). Crew observations of the lunar surface revealed that there was no readily discernible boundary between the overlying thin regollth and the dark mantling material. The thickness of the dark mantlingmaterial was estimated to be between 5 and 10 m (ref. 10-3). As pointed out earlier, whether the dark mantling matetial/subfloor interface represents a sharp seismic discontinuity or is gradational cannot be determined because the shortest explosive-charge-to-receiver distance was approximately 100 m. The dominant rock type observed underlying the dark mantling material is a mediuna-grained vesicular basalt believed to be primarily mare-type basalt. Crew observations of the crater walls revealed textural variations that suggest the involvement of individual flow units. Seismic observations have indicated 248 m of 250-m/sec material overlying 927 m of 1200-m/sec material, The abrupt change in seismic velocity from 250 to 1200 m/sec and, by inference, in other physical properties suggests a major change in the nature of the evolution or deposition of the Apollo 17 subfloor basalts. However, a similar range of seisrrric velocities has been observed with refraction surveys on terrestrial lava flows. Some insight can be gained by considering specific lava flows that have been exam-

10-1 1

ined in some detail as possible lunar analogs: the Southern Coulee, the SP flow, and the Kana..a flow (refs. 10-12 and 10-13). The Southern Coulee is a recent lava flow near the Mono Craters in eastern California. Seismic velocities range from 160 m/sec at the surface to 2000 m/sec at depth. The higher velocities are found in more competent, denser lava that underlies higher porosity, lower density surface material. The SP flow is a blocky basalt flow located in the northern part of the San Francisco volcanic field near Flagstaff, Arizona. Vesicularity ranges from 5 to 50 percent, and in situ seismic velocities range from 700 to 1100 m/sec. The Kana-a flow, also located near Flagstaff, is an olivine basalt flow intermingled with ash; seismic velocities range from 700to 1200 m]sec. Observed velocities on terrestrial lava flows b:racket the velocities measured at the Apollo 17 site and therefore support the presence of lava flows in file Taurus-Littrow valley. Whether the 250-m/sec w,qocity is representative of a separate flow or is merely the manifestation of shattered near-surface basalts mixed with pyroclastic materials cannot be resolved from the seismic data. Nevertheless, a surface layer of fractured, loose, blocky material merging into more welded flows is a common occurrence on Earth. Photographs of the walls of Hadley Rille (ref. 10-14) also attest to the blocky nature of the near-surface mare basalts. Because of the similarity in structure and the analogous seismic velocities on the Earth and the Moon, the sum of the 248 m of 250-m/sec material and 927 m of 1200-m/sec material, 1175 m, is designated as representing the full t]_ckness of the subfloor basalts at the Apollo 17 site. The material underlying the basalts with a seismic velocity of _ km/sec is difficult to classify by rock type. Based on the geological evidence, it seems likely that the highland massif material that rings the narrow, grabenlike valley at the Apollo 17 site underlies the basalt flow or flows. Several rock types were recognized in the North and South Massifs, but the dominant rock type is apparently a coherent breccia believed to be similar to the breccias sampled at the Apennine Front (Apollo 15) and at Descartes (Apollo 16). Laboratory velocity measurements have been reic_rted for two Apollo 15 breccias, 15418 and 15015 (ref. 10-15). Sample 15418 is described as a dark-gray breccia of chemical composition similar to that of anorthite-rich gabbro. Sample 15015 is a more friable

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breccia of unknown composition. The in situ value of km/sec is close to the seismic velocities measured in the laboratory figure 10-16. for sample 15015 and shown in

CONCLUSIONS Before the Apollo 17 mission, the question of how the P-wave velocity increased from 100 to 300 m/sec near the surface (refs. 10-16 to 10-19) to _6 km/sec at a depth of 15 to 20 km (ref. 10-2)was unexplained. The main reason for the uncertainty was the gap in traveltime data between the range of a few hundred meters (previous active seismic experiments) and 67 km (Apollo 14 LM impact as recorded by the Apollo 14 passive seismic experiment). The Apollo 17 lunar seismic profiling results have demonstrated that the seismic velocity increases in a sharp stepwise manner in the upper 2.5 km. A surface layer with a seismic velocity of 250 m/see overlies a layer with a velocity of 1200 m/sec. Beneath the 1200-m/sec layer, the seismic velocity increases sharply to 4000 m/see. The velocities of 250 and 1200 m/sec agree with those observed for basaltic lava flows, indicating a total thickness of approximately 1200 m for the infilling mare basalts at Taurus-Littrow. When the Apollo 17 results are combined with earlier traveltime data for direct and surface-reflected seismic arrivals from LM and SIVB impacts (ref. 10-2), it will be possible to construct a velocity model for the upper lunar crust believed to be representative for a mare basin. Such work is now underway,

The impacts of the SIVB and the lunar module (LM) ascent stage of the Apollo 17 mission concluded a series of nine such impacts from which seismic signals have been recorded by the Apollo seismic network. The network includes stations installed at the landing sites of the Apollo 12, 14, 15, and 16 missions and spans the near side of the Moon in an approximately equilateral triangle with 1100-kin spacing between stations. (The Apollo 12 and 14 stations are 181 km apart at one corner of the triangle.) The oldest of these stations, Apollo 12, has now operated for more than 3 yr, and the entire network has been in operation for 1 yr as of April 1973. Four seismometers are included at each station: three low-frequency components forming a triaxial set (one sensitive to vertical motion and two sensitive to horizontal motion) with sensitivity to ground motion sharply peaked at 0.45 Hz, and a fourth seismometer sensitive to vertical motion with peak sensitivity at 8 Hz (high-frequency component), These instruments can detect vibrations of the lunar surface as small as 0.05 nm at maximum sensitivity, Of the 16 separate seismometers, all but two are presently operating properly. The hilgh-frequency component at the Apollo 12 station has failed to operate since initial activation, and one of the low-frequency seismometers at the Apollo 14 station (vertical component) became unstable after 1 yr of operation. Moonquakes have been detected by the lowfrequency seismometers of each station at average rates of between 600 and 3000 per year, depending on the station; all the moonquakes are quite small by terrestrial standards (Richter magnitude 2 or less), Thousands of even smaller moonquakes are detected aThe University of Texas at Galveston. Institute of Technology. tPrincipallnvestigator,
bMassachusetts

by the high-frequency seismometers. Meteoroid impacts are detected by the low-frequency seismometers at average rates of between 70 and 150 per year. Although less numerous than moonquakes, meteoroid impacts generate the largest signals detected. Several criteria have been useful in distinguishing moonquake signals from meteoroid impact signals. The most useful are the character of shear waves and the time interval from the beginning of a signal to its maximum amplitude (the signal rise time). Moonquake signals have impulsive shear wave arrivals and short rise times relative to those of impact signals. In addition, many of the moonquake signals can be grouped into sets of matching events; signals of each set have nearly identical waveforms. Signals from meteoroid impacts cannot be matched with one another. Analysis of the seismic signals from the manmade impacts and from natural sources has led to a model for the Moon that is quite different from that of the Earth. Refinements in the present lunar model can be expected as data accumulate from natural events. In this report, the major findings to date from the passive seismic experiment are summarized. STRUCTURE AND STATE OF THE LUNAR INTERIOR The surface of the Moon is covered by a highly heterogeneous zone in which, because of the nearly complete absence of volatiles; seismic waves propagate with very little damping. Scattering in this zone accounts for the prolongation of lunar seismic signals and for the complexity of the recorded ground motion relative to typical terrestrial signals (refs. 11-1 and 11-2). Most of the scattering occurs in the outer several hundred meters, but significant scattering may occur to depths as great as 10 to 20 km. The tl..1

11-2

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"granularity" within the scattering zone ranges from micron-size fragments to heterogeneity on a scale of at least several kilometers. The roughness of the lunar surface undoubtedly contributes to the scattering of seismic waves, Some find the combination of intensive scattering and low damping of seismic waves to be confusing because, on Earth, scattering is normally associated with a high degree of damping. However, these can be regarded as independent phenomena. On Earth, the presence of water is the dominant factor in dissipation of seismic energy at shallow depth; scattering results if heterogeneity is present on a scale comparable to the signal wavelengths. In the outer shell of the Moon, heterogeneity results in scattering, but it is the nearly complete absence of water (or any other fluid), and the consequent high transmission efficiency (low damping), that leads to the extreme prolongation of lunar seismic signals, Knowledge of the lunar structure below the scattering zone is derived mainly from analysis of seismic signals from impacts of Apollo space vehicles of two types: the LM ascent stage and the SIVB stage of the Saturn booster. Each LM was guided to impact following the return of the surface crewmen to the command and service module in lunar orbit. Following separation from the Apollo spacecraft, the SIVB stages were directed to planned impact points by TABLE 11-1.-Coordinates, Distances

remote control from Earth. Nine impacts were accomplished successfully. Seismic signals from these impacts were recorded at ranges from 67 to 1750 kin. Impact coordinates and the distances and azimuths from the receiving stations are listed in table 11-I. The Apollo 17 LM impact was also recorded by the geophones of the active seismic experiment, located at the Apollo 17 landing site, at a range of 9 kin. These data, combined with data from high-pressure laboratory measurements on returned lunar samples, provide information on lunar structure to a depth of approximately 150 km. Information on lunar structure below this depth is derived principally from analysis of signals from deep moonquake and distant meteoroid impacts. Analysis of the manmade impact data has revealed a major discontinuity at a depth between 55 and 65 km in the eastern part of Oceanus Procellarum (refs. 11-3 and 11-4). By analogy with the Earth, the zone above the discontinuity is called the crust and the zone below, the mantle. Whether the crust is regional or is a global feature cannot be determined from the present seismic network. However, the early formation of a crust by igneous processes on a global scale would appear to explain such observations as the unexpectedly high heat flow (ref. 11-5) and the presence of large-scale petrological provinces inferred from orbital X-ray fluorescence data (ref. 11-6) and from lunar sample analysis. The and Azimuths
Distance and

aListed coordinates are derived from the Manned Space Flight Network Apollo tracking data. Locations based on these data are referenced to a mean spherical surface and may differ by several kilometers from coordinates referenced to surface features. bPtemature toss of tracking data reduced the accuracy of the estimate. The listed coordinates for this impact are estimated from seismic data.

PASSIVE SEISMIC EXPERIMENT velocity of compressional waves in the lower half of the crust is between 6.3 and 7.0 km/sec, a velocity range appropriate for the aluminous basalts and gabbroic anorthosites that predominate in the lunar highlands sampled thus far. Thus, the most plausible hypothesis is that a widespread crust, formed early in the history of the Moon, outcrops in the present lunar highlands. The thickness of the crust is likely to vary greatly. There is some evidence for a discontinuity within the crust at a depth of 25 km that may define the base of the mare basalts in Oceanus Procellarum (ref. 11-3). Below the crust, a relatively homogeneous zone extending to a depth of approximately 1000 km is suggested by the nearly constant velocity of seismic waves. The average velocity of compressional waves in the homogeneous zone is approximately 8 km/sec. A slight decrease in velocity with depth probably occurs in the lower half of this zone. Very low attenuation of both compressional and shear waves in this zone precludes the presence of any appreciable melting, Poisson's ratio is approximately 0.25 at the top of the mantle, A striking contrast has been found between signals that originate on the near side of the Moon and those from far-side sources. Direct shear waves, normally prominent in signals from near-side moonquakes and weakly defined in near-side meteoroid impact signals, cannot be found in the seismograms recorded at several of the seismic stations from far-side events, For example, as shown in figure 11-1, shear waves from a large meteoroid that struck the far side near the crater Moscoviense arrive at the Apollo 15 station at the expected time, but they are missing at the Apollo 14 and 16 stations when expected. Much later phases arrive at these stations at times predicted for surface-reflected shear waves (SS) that travel through the upper mantle of the Moon. Similarly, shear waves from far-side moonquakes that can be identified at the Apollo 15 and 16 stations are missing at the Apollo 14 station (fig. 11-2). Although available data are not sufficient to derive a detailed seismic velocity model for the deep interior, these observations can be explained by introducing a "core" with a radius between 600 and 800 km in which shear waves either do not propagate or are highly attenuated (dissipation factor Q of approximately 100 or less)(ref. 11-7). The compressional wave velocity within this zone may be slightly lower than that in the mantle. The maximum

11-3

allowable velocity decrease for compressional waves is approximately 0.3 km/sec. The term "core" as applied in this discussion is not meant to imply a major compositional or structural discontinuity as it does for the Earth. In the lunar case, it is simply a central zone in which the characteristics of seismic wave transmission differ from those in the surrounding material. However, the presence of a small "inner" core in the terrestrial sense is not precluded by present data. Seismic wave attenuation is strongly temperature dependent, showing rapid increase with increasing temperatures and increasing sharply with the onset of melting (ref. 11-8). Thus, temperatures approaching the solidus (melting point) in the lunar interior may account for the lack of shear wave transmission indicated by the seismic data. Assuming an interior of mafic silicate composition, this state would require temperatures of between 1700 and 1900 K at a depth of approximately 1000 km. This model is in substantial agreement with several thermal models recently proposed by Toksoz et al. (ref. 11-9). Partial melting of silicate material is considered to be a possible cause of the low Q, low-velocity zone of the upper mantle of the Earth (refs. 11-8 and 11-10). A completely molten core of the size indicated, however, is not likely because a decrease of the compressional wave velocity exceeding the value of 0.3 km/sec obtained by the preliminary analysis would be expected. Other possibilities, such as increased volatiles in the deep interior of the Moon, cannot be eliminated at present. The possibility of a high-density, molten metallic core similar to that of the Earth is eliminated by both moment-of-inertia and seismic-wave-velocity considerations. The radius of approximately 700 km is too large for such a core. By analogy with the Earth, the lithosphere-the relatively rigid outer shell of the Moon-can be considered to be approximately 1000 km thick. The core of the Moon is equivalent to the asthenosphere (low-velocity zone) of the Earth. MOONQUAKESAND Thermal LUNAR Moonquakes TECTONISM

'Thousands of small seismic signals have been detected by the high-frequency seismometers at the Apollo 14, 15, and 16 stations. (The high-frequency

1 1-4

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Apollo 15 station

tSSI

4 Hz Apollo 14 station .......... -_-_:_ i

I I

,

,

? Hz .

FIGURE ll-1.-Ffltered short-period seismograms of seismic events detected on July 17, 19"/2. The signal is believed to be from a meteoroid impact on the far side of the Moon. Traces for two different filter settings are shown for each station. The frequencies given, 4 and 2 Hz, are the center frequencies of the narrow band-pass filters used in the data playback. The I indicates the estimated time of impact; P, the observed arrival time of the direct compressional wave; and S, the expected arrival time of the direct shear wave. Note that the eharacteristie shear wave bulge, clearly visible at the Apollo 15 station, is missing at the Apollo 16 and 14 stations when expected. A digital unit (DU) is the signal variation that corresponds to a change in the least significant bit of the 10-bit data word. seismometer at the Apollo 12 station failed to operate.) These signals are not recorded by the low-frequency seismometers because of the restricted bandwidth of these instruments. The high-frequency signals are generated (1) by thermoelastic stresses within the LM descent stage and other equipment left on the lunar surface at each site, (2) by small meteoroid impacts at near ranges (a few tens of kilometers and less), and (3) by small moonquakes (micromoonquakes) that originate within a few kilometers of each station. Micromoonquake activity begins abruptly approximately 2 days after lunar sunrise and decreases rapidly after sunset (ref. 11-2). These events are recognized by the repetition of nearly identical signals, implying a highly localized source for each set. Forty-eight sets of matching rnicromoonquake signals have been identified at the Apollo 14 station, and 245 sets at the Apollo 15 station. Micromoonquake activity at the Apollo 16 station is very low in comparison with that at the Apollo 14 and 15 stations. Signals of each set occur at monthly intervals, usually one event per month per

FIGURE 11-2.-A comparison of signals from selected moonquakes detected at the Apollo 14, 15, and 16 stations. One of the four moonquakes (Oct. 11, 1972) is common to all three stations. The signals were too weak to be detected at the Apollo 12 station. Only the horizontal-component seismogram is shown for each event at each station. These moonquakes originated at the same point within the fax half of the Moon. Note that the shear wave is not observable at the Apollo 14 station when expected (marked "S expected"). The P-wave at the Apollo 16 station is too weak to be identified with confidence. set, and at the same time relative to sunrise to within a few hours. The strong correlation with sunrise and sunset indicates that micromoonquakes are of thermat origin, Two possible source mechanisms for thermal moonquakes are suggested: (1) cracking or movement of rocks along zones of weakness and (2) slumping of soil on lunar slopes triggered by thermal stresses. The characteristics of the signals imply that motion is always in the same direction and that some thermal moonquake sources change position slightly from one lunar day to the next, but the source mechanism is not yet understood, Forty-one categories of matching events have been recognized thus far. As in the case of thermal moonquakes, the repetition of seismic signals of identical waveforms indicates that the point of origin remains f'txed probably to within a few kilometers. Thus, there are at least 41 active zones within the Moon at which moonquakes originate. Seismic signals from these focuses represent only 10 percent of the total number of signals believed to be of moonquake origin based on their signal character. Thus, the existence of many more focuses from which the signals are too small for detailed waveform comparison is likely. Peaks in moonquake activity occur at biweekly intervals corresponding to the apogee/ perigee cycle, as shown in figure 1 1-3 for the Apollo 14 station. A 7-month variation in activity, corresponding to the solar perturbation is also apparent in such plots. of the lunar orbit, If the activity is

Distant

Moonquakes

Moonquakes detected by the low-frequency seismometers of each station were soon recognized as being distant from all stations. The characteristics of the low-frequency moonquake signals are also quite different from those of the locally generated moonquakes described previously. With a few possible exceptions, all low-frequency moonquake signals that are large enough to examine in detail cau be grouped into sets of matching events. Events of each set occur at monthly intervals, usually once per month, with longer term variations in the moonquake magnitudes,

examined at a given moonquake focus, as shown in figure 1 1-4 for the active zone designated A_, not only the monthly and 7-month cycles but also a longer term variation can be recognized. The longer term variation may correspond to the 6-yr term in the variation of lunar gravity. These correlations strongly suggest that tides are the dominant source of energy released as moonquakes. It is possible, in fact, likely, that a small secular component of stress, introduced

11-6

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(_

_ 30F

_

_

_-20 F/'-------._.I_'_---o
001- 15_ _ _ . ""_*,

f--.J_
_ h

,
_A

_

/'---_.
A l _ _"'--.

,_ _"h"_"_-. _-''''-'_

_E

1971 _ Nodical months

1972

FIGURE 11-3.-Moonquake activity recorded at the Apollo 14 station between February 7, 1971, and July 27, 1972, showing the number of moonquakes detected per day. Peaks in activity occur at 2-week intervals corresponding to the apogee/perigee cycle. A longer term variation in moonquake activity, with a period of 206 days, is also seen in the smoothed activity plot shown above the daily count. This 206-day period corresponds to the period of the tidal variation introduced by solar perturbation of the lunar orbit.

131211

I

206 days

'I I'
206days

io
7

,I

0 t96' @

1970

,

I, i

1970_ _ 1971

,,

1972

FIGURE ll-4.-History of occurrence of category A_ rhoonquakes as recorded at the Apollo 12 station between November 1969 and January 1972. The length of each bar is proportional to the maximum amplitude of the recorded signal. Monthly and 206-day cycles are evident in this plot together with a longer term variation that may correspond to the 6-yr variation in tidal stress. possibly by the recession of the Moon from the Earth or by heating or cooling of the lunar interior, is also present, The distribution of moonquake epicenters located thus far is shown in figure 11-5. In this distribution, two narrow belts of activity lying approximately along arcs of great circles are recognized. The western belt runs approximately north-south over a lengthof at least 2500 km. The eastern belt trends northeastsouthwest over a length of at least 2000 kin. The focuses of these events are concentrated at depths of 800 to 1000 kin, as shown in figure 11-6. Earlier suggestions of possible correlations and mare rims are no longer creased data now available, between moonquakes supported by the inlithosphere) immediately above a relatively weak central zone (the asthenosphere). If this model is correct, then the depth of the moonquake zone may simply be a consequence of the differing yield strengths of the material within these two zones. Slow changes in the shape of the Moon, in response to time-varying tidal stresses, will produce stress concentrations at the lithosphere/asthenosphere boundary. When the stress exceeds the shear strength of the material, rupture will occur. The availability of fluids migrating upward from a partially molten zone would also facilitate dislocation in the lunar lithosphere. The narrow alinement of moonquake focuses in long, belts is more difficult to understand. These of large-scale variations in of the material of the

According to our present model, moonquakes occur at the base of a thick, rigid shell (the

belts may be a consequence the mechanical properties

PASSIVE

SEISMIC

EXPERIMENT

11-7

FIGURE ll-5.-Map showing the locations of the Apollo seismic network stations and of 26 moonquake epicenters. The epicenters are the points on the surface immediately above the active zones (focuses) in which moonquakes originate. Sofid circles indicate focuses for which the depth of the focus can be determined. Open circles correspond to cases in which data are not sufficient for determination of depth. A depth of 800 km has been assumed in these cases. The number at each epicenter is an arbitrary identification code used by the experiment team. Note that in two cases (epicenters 1 and 6 and epicenters 18 and 32) the epicenters are so closely spaced that their separation cannot be distinguished at the scale plotted. lithosphere or of the asthenosphere. They may, for example, be zones of increased temperature or they may reflect compositional heterogeneity. Alternatively, the moonquake belts may be manifestations of weak, large-scale convective motions or they may be residual stress dating from the time of formation of the Moon. The belts do not appear to lie alonglarge, continuous fractures, because the orientation of tidal

11-8

APOLLO 17 PRELIMINARY SCIENCE REPORT 0 ,,///////////////////////////A_C !//_//////////////////////////_ _r_ui must be approximately heat production. equal to the rate of internal

200

METEOROID

FLUX

4o0 Lithosphere 6o0 __, "--7 _" 800 I _-

Seismic signals detected by the Apollo seismic network from meteoroid impacts appear to be generated by objects in the mass range from 100 g to 1000 kg. Results obtained to date have been derived by a method using only the statistical distribution of maximum amplitudes of seismic signals recorded from meteoroid impacts (ref. 11-2). The average flux estimated from data of more than 1 yr is log N= -1.621.16 log m where N is the cumulative number of meteoroids of mass m (in grams) and greater that strike the Moon per year per square kilometer. This flux estimate is 1 to 3 orders of magnitude lower than that derived from earlier Earth-based measurements. Our estimate is lower than the average flux estimated from the distribution of crater sizes on the youngest lunar maria. This flux is consistent with a hypothesis that the population of small fragments in the solar system decreases with time as the fragments are gathered up by collisions with the planets. The seismic data predict that a

, [

1000

:_:_:

I

1200

1400

16000

1

2

3 4 5 6 7 Number fm0onquakes 0

8

9

10

meteoroid of 7 to 10 kg mass can be detected by the least sensitive station (Apollo 12) from any point on the Moon. Approximately 50 percent of the impacts detected by a station occur more than 1000 km from the station. The total data appear to contain at least two distinct meteoroid populations: the normal fragment distribution that varies little throughout the year and a population of relatively large objects that intersect the lunar orbit from April through July each year. Because the latter are detectable seismically from anywhere on the Moon, the Apollo seismic network affords greater exposure to these rare events than any other method of measurement. SO M M A R Y AN D C ON C LUSI ONS Seismic activity within the Moon is extremely low compared to that within the Earth. The Moon is characterized by a rigid, dynamically inactive outer shell, approximately 1000 km thick, surrounding a core that has markedly different elastic properties. Current moonquake activity is concentrated near the boundary between these two zones. It is likely that temperatures within the lunar core are at, or near, the temperature of the beginning of melting (solidus

FIGURE ll-6.-The depth distribution of moonquakes for which present data are sufficient for determination of focal depths (18 cases). Question marks in the zone labeled "asthenosphere" indicate that present data arenot sufficient to define the inward extent of this zone. The asthenosphere, in which partial melting is believed to occur, may extend to the center of the Moon or it may be restricted to a thin shell at a depth of approximately 1000 km. stresses leading to moonquakes varies greatly among the focuses of a given belt. Thus, varying orientations of the dislocation planes are implied. Further speculation on the possible origin of the zones of moonquake activity is postponed until the zones can be delineated with greater certainty. Surface features that appear to be tensional have been taken as evidence of slight past expansion as the lunar interior grew warmer. However, lack of moonquakes at shallow and intermediate depths suggests that, presently, the Moon is neither expanding nor contracting at an appreciable rate. Hence, the Moon must be close to thermal equilibrium at the present time; that is, the rate of heat flow out of the Moon

PASSIVE

SEISMIC EXPERIMENT

11-9

point) and that the core .is much weaker than the outer shell. If so, the outer shell may be regarded as the lunar lithosphere and the weak central zone as the asthanosphere. The transition between these zones appears to be quite gradual. Thus, the term "core" is not meant to imply a major structural or compositional discontinuity as it does for the Eartlh. However, the presence of a true core, in the terrestrial sense, somewhere below the lithosphere/asthenosphere boundary is not precluded by present data. The great thickness of the lunar lithosphere relative to that of the Earth probably accounts for the widely indicates differing that the

The primary objective of the lunar surface gravimeter (LSG) is to use the Moon as an instrumented antenna (refs. 12-1 to 12-8) to detect gravitational waves predicted by Einstein's general relativity theory. A secondary objective is to measure tidal deformation of the Moon. Einstein's theory describes gravitation as propagating with the speed of light, Gravitational waves carry energy, momentum, and information concerning changes in the configuration of their source. In these respects, such waves are similar to electromagnetic waves; however, electromagnetic waves only interact with electric charges and electric currents. Gravitational waves are predicted to interactwithall forms of energy, The visible light, radio, and X-ray emissions, together with the cosmic rays, are the sources of all our present information about the universe. Gravitational radiation is a totally new channel that would be capable of giving information about the structure and evolution of the universe, BASIC THEORY It is possible to study many forms of energycarrying waves by generating and detecting them in the laboratory. At present, this type of study is not feasible for gravitational radiation. The ratio of mass to electric charge for elementary particles is so small that only 1 graviton is emitted for every 1043 photons in ordinary laboratory experiments. Only objects the size of stars or galaxies can generate enough gravitational radiation to be detected by present apparatus. Detailed mathematical analysis using Einstein's equations has shown that an elastic solid would serve as a gravitational radiation antenna. Dynamic forces associated with the gravitational waves set up internal auniversity of Maryland.
"}'Principal Investigator.

vibrations in the antenna. These forces are somewhat similar to the gravitational forces that cause the tides. Observation of internal vibrations is limited by noise. If gravitational waves of sufficientlyhighintensity covering certain bands of frequencies are incident on the Moon, internal vibrations of the Moon will be excited. These vibrations may cause oscillatory surface accelerations. Theory predicts that only the lowest allowed frequency and certain overtones can be excited in this way. The kinds of vibrations that are excited by gravitational waves are believed to have symmetry. Thus, the "breathing" mode of the Moon, in which all points of the lunar surface move outward together, and half a cycle later, all points move inward together, is not expected to be driven by gravitational radiation. However, the "football" mode :is expected to be excited by gravitational radiation. In the "football" mode, all points on the lunar equator move outward at the same time that points on the lunar poles are moving inward. Half a cycle later, _fll points on the equator are moving inward while the polar regions are moving outward. Very little is known about possible sources of gravitational radiation. An object may emit considerable gravitational radiation and have very little emission of light and vice versa, At present, the search tbr this radiation must be made by developing the best possible instruments and operating them at the limits of sensitivity. Approximate estimates suggest that present procedures have a fair chance ofobserving real effects by using the Moon because of the relative quiet of the hmar environment. The Earth is also an instrumented antenna, but it has a high level of noise because of the atmosphere, the oceans, and seismic activity. Quiet periods exist when it may be possible to observe the coincident response of the Earth and Moon to gravitational waves. The surface acceleration of the Earth is measured with a somewhat similar gravimeter and recorded as a function of time. Comparisons between 12-1

12-2

APOLLO ] 7 PRELIMINARY SCIENCE REPORT

the lunar and terrestrial records should allow searches for simultaneous sudden surface accelerations. delaying one recording relative to the other one, rate of chance coincidences may be measured. significant excess of zero-delayed as compared time-delayed (chance) coincidences can establish existence of correlations. By the A to the

Experiments have been conducted in the kilohertz region using aluminum cylinder masses of several thousand kilograms that are isolated from terrestrial effects. The existence of such coincidences has been established using antennas at the University of Maryland and at the Argonne National Laboratory near Chicago, Illinois. The high frequency (seismic outpu0 of the LSG will be compared with the records of the aluminum cylinder experiments in an effort to find numbers of coincident amplitude increases over and above the chance rate. The LSG was also designed to measure the tidal effects on the Moon and to serve as a one-axis seismometer. The lunar orbit is slightly elliptical, and the Moon undergoes librations. For these reasons, the gravitational fields of the Earth and Sun sensed by a given part of the lunar surface will vary with time. This variation results in time-dependent tidal forces on the Moon. The figure of the Moon will be distorted in consequence of the tidal forces, and the amount of this distortion gives information internal composition of the Moon. EOU IPM E NT The LSG (fig. 12-1)was emplaced on the Moon by the Apollo 17 crew. This instrument is a sensitive balance with a mass, spring, and lever system and with electronics for observation of accelerations in the frequency range from 0 to 16 Hz. The LSG has a nominal sensitivity of approximately one part in 10 xl of lunar gravity, A schematic diagram of the spring-mass suspension system is shown in figure 12-2. In the instrument, the major fraction of the force supporting the sensor mass (beam) against the local gravitational field is provided by the zero-length spring. A zero-length spring is one in which the restoring force is directly proportional to the spring length; such a spring is very useful in obtaining a long-period sensor (ref. 12-9). Small changes in force tend to displace the beam up or down. This imbalance is adjusted to the null position by repositioning the spring pivot points by about the (/ FIGURE 12-1.-Lunar surface gravirneter.

Massadding mechanism FIGURE 12-2.-Scheraatic diagram of the lunar gravity sensor. use of micrometer screws. The sensor mass is modifled by the addition or removal of small weights, permitting the range of the sensor to be extended from Earth testing to lunar operation. The electronic sensing portion of the instrument consists of a set of capacitor plates. Two plates, which are part of a radio-frequency bridge circuit, are fixed to the frame of the sensor and are geometrically concentric with a

LUNAR SURFACE GRAV[METER EXPERIMENT third plate of similar size, which is attached to the movable beam of the sensor. The plates are so arranged that the center plate is located exactly between the two outer plates when the beam is exactly horizontal. If the force on the mass changes, it tends to move the beam, and the resulting bridge unbalance creates an ac error voltage. This voltage is amplified and rectified with the size of the output voltage determined by the direction of the displacemeat. A fixed de bias voltage is applied to the capacitor plates balanced with respect to ground, and these plates are also connected to the rectified error voltage. If the error voltage is zero, the balanced bias plate voltage produces equal and opposite electrostatic forces on the mass. If a positive error voltage is present, the voltage applied to one plate is increased and the voltage applied to the other plate is decreased. The resulting force tends to restore the mass to its originally centered position. This rectified voltage is a measure of the changes in surface acceleration. The mass does not follow fast changes, However, the fast-changing servomechanism error voltage is a measure of the rapidly changing componears of the surface acceleration, The LSG can also be operated with the voltage output not fed back to restore the beana to equilibrium. As indicated in figure 12-3, the different configurations have different responses to surface accelerations, The data cover the frequency range fl'om 0 to 16 Hz in three bands. The rectified integrated error

12-3

voltage over the range dc to 1 cycle per 20 re.in gives information on the lunar tides. A tilter with amplification covers the range from 1 cycle per 20 rain to 3 cpm. Another tilter amplifies the fast components in the range from 3 cpm to 16 Hz. The latter range is of interest for seismology and for search for highfrequency gravitational radiation from sources such as the pulsars. The complete response function of the sensor and electronics for several different configurations is given in figures 12-3 and 12-4.

THERMAL

CONTROL

The gravimeter uses a metal spring with a force constant that is, in general, temperature dependent. There are two temperatures at which thermal effects are minimal; for the LSG, one of these occurs near 323 K. To obtain the required performance, it is necessary to control the temperature of the spring to within better than 1 mdeg near the optimum temperature throughout the lunar day/night cycle. Therreal control is accomplished by use of thermal insulation, which limits heat exchange with the lunar surface. A hole in the top of the LSG radiates heat to the cold sky so that an internal heater is required to maintain the 323 K temperature sensed by thermistors. A sunshade prevents the solar heat from directly entering the LSG. The sunshade is tilted at an angle corresponding to the latitude of the emplaced instruments. The thermal control system has controlled the temperature of the spring to within 1 mdeg.

FIGURE 12-6.-Power spectrum analysis of lunar sunrise data. When the LSG was emplaced, it was impossible to balance the beam by sending commands to add or subtract mass. The motion of the beam suggested that an additional force corresponding to lunar gravity acting on approximately a gram of mass would balance the beam. Such a force can be exerted by operating the mass-changing mechanism beyond the point of addition of all masses so that it contacts the beam, moving it to midposition. In this configuration, the instrument is apparently behaving like a gravimeter with resonances at 1.5 Hz and possibly at a much lower frequency. The seismic output appears to be that corresponding to the sensitivity indicated in figure 12-4, and noise output in the free modes open-loop band (fig. 12-3) suggests that surface accelerations are being sensed in these bands of frequencies. The seismic channel output during a several minute period associated with lunar sunrise is

The primary goal of the traverse gravimeter experiment (TGE) was to make relative gravity measurements at a number of sites in the Apollo 17 landing area and to use these measurements to obtain information about the geological substructure. A secondary goal was to obtain the value of the gravity at the landing site relative to an accurately known value on Earth. Both these goals were successfully achieved by the experiment. A gravity tie has been obtained between the Taurus-Littrow landing site and the Earth with an estimated accuracy of approximately 5 regal. Relative gravity measurements that can be used to infer the substructure of the area have been obtained at stations visited during each period of extravehicular activity (EVA). BASIC THEORY Free-Air and Bouguer Anomalies

distances of these stations from the center of the Moon. If gm denotes the gravity at the surface of the Moon, M the mass of the Moon, r the radius of the Moon, and k the universal constant of gravitation, then = kM "7 2, (13-1)

gm

The free-air gradient then is _=agm --=-2k/4 _-2gm Dr r s r (13-2)

and the free-air correction is 2gm/r, which yields a value of 0.19 mgal/m. The elevation in meters is measured from an arbitrary elevation datum (fig. 13-1). The free-air correction is added to the relative gravity values to obtain the free-air anomalies. The next step in the interpretation of the free-air anomalies involves the Bouguer correction. The Bouguer correction allows for the gravity effect (i.e., the vertical component of the gravitational attraction) of the material above the elevation datum

The basic theory for the interpretation of the traverse gravity measurements can be described with the help of the sketch in figure 13-i. As a simplifying approximation, two-dimensionality is assumed; the sketch is a hypothetical geological cross section. The gravity measurements are made at the lunar module (LM) landing site and at certain stations (stations 1, subtracted from the values at the other stations, and, 2' 3' 4' 5' etc')" The gravity value at the LM site is for this report, only the relative values at the stations will be considered. in the interpretation of the relative The first step gravity values is to make the free-air correction for elevation; that is, to allow for the differences in the

computed at the gravity stations. This correction involves a knowledge of the density of the material above the elevation datum. In the sketch in figure 13-1, densities of Pl for the material comprising the massifs and P2 for the material of the valley floor have been assumed. The fact that the actual situation can be much more complicated must be considered in the interpretation of the Bouguer anomalies. In gravity interpretation, the Bouguer correction is usually applied in two steps. The first, the flat-plate Bouguer, assumes that the elevation is the same at all points as at the station where the correction is being applied. The second, the terrain correction, allows for the departure of the actual terrain from a plane at the height of the station. For the Taurus-Littrow landing site, the terrain corrections are large, and no particular advantage is gained by computing the flat-plate Bouguer corrections and the terrain corrections separately. By computing the gravity effect of all the material above the elevation datum with a single computation, the combined Bouguer correction is applied, and, by adding it to the free-air anomaly, the Bouguer anomaly is obtained. In these calculations of the Bouguer corrections, a flat Moon rather than a spherical Moon is used. The relative error at the different stations is negligible for the present calculations. The final step is the interpretation of the Bouguer anomalies. The Bouguer anomalies have allowed for the elevation differences between the different stations and for the gravitational effect of the material above the elevation datum. Therefore, the Bouguer anomalies are interpreted in terms of, and provide information about, the density contrasts of rocks lying below the elevation datum. In the simplified model shown in figure 13-1, for instance, the density contrast Pl - 92 between the material comprising the massifs and the material lying below the valley floor gives rise to the Bouguer anomalies at the stations, The actual structural situations as well as the density variations are probably much more complicated than those shown in the sketch. The interpretation approach will be to work with simple models consistent with available geological information and to see how these models explain the gravity data. The final structural solution will be constrained by the gravity results, by considerations of geological plausibility, and by the results from the other geological and geophysical data.

As a first approximation, two-dimensionality is assumed. The gravity effect of a body is obtained by approximating its cross section by an irregular polygon. The gravity effect of a body with a polygonal cross section has been given by Talwani et al. (ref. 13-1).

Three-Dimensional

Calculations

For more careful analysis of the gravity data, it is essential both to compute the Bouguer anomalies and to interpret them without the assumption of twodimensionality. The basic formula used in this calculation is the gravity effect of a vertical prism, which is given by Jung (ref. 13-2). For distant areas, prisms of large area can be chosen and an average elevation assumed for them. For closer areas, prisms of smaller area must be chosen. By actual trial and error, prisms of optimum area are chosen at various distances from the landing site for use in the calculations. Such a determination has been made. The three-dimensional calculations are not complete at the present time, and only the results of two-dimensional be discussed in this report. EO.UIPM ENT Sensor The gravity sensor used in the TGE is a Bosch Arma D4E vibrating string accelerometer (VSA). The accelerometer is schematically shown in figure 13-2. Each of the two strings, when energized, generates continuous vibrations with its own frequency, the value of which depends on the value of g. The difference between the two frequencies can be obtained. The difference frequency between the two strings Af n when the sensor is in its normal vertical position can be written as lXfn = k ° + klg
+

calculations will

k292

+

k393 +

...

(13-3)

Terms of order higher than 3 can be neglected. Nominal values for k o, kl, et cetera, for the flight vibrating string accelerometers are k0 = 7 Hz, k_ = 129 Hz/g, k2 = -0.00034 Hz/g 2 , and ka = 0.003 Hz/g a . A principal reason for the use of a doublestringed rather than a single-stringed instrument is the

TRAVERSE GRAVIMETER EXPERIMENT

13-3

...... - Magnet _i[ _'_ .... ...-Strir, g l C"..... .,--Mass l

The electrically conducting VSA strings are placed Filtering and Phase Lock Loop voltage is applied across the string, the resulting in a permanent magnetic field (fig. 13-2). When a current causes motion of the string and induces a voltage across the string. The voltage is regenerated the string. through output of high-gain amplifieris and fedwave ofto The a stable, each VSA string a sine back a frequency between 9.25 and 9.75 kHz. The signal is

Input axis

........... ........... , _'"-'_ ............

Crosssupport Soft: pring s

Mass2

phase lock loop module are to determine the difference frequency between the outputs of the two fed to a phase lock loop module. The purposes of the tions from the resultant signal.

ii.iiii?i!i. _i .......... String2

Should any vibrations from the VSA to exceed a phase lock loop alarm strings and to filter the

cause the input frequency a previously specified limit, is generated. This alarm is effect of undesirable vibra-

indicated by the TGE display. FIGURE 13-2.-Schematic viewof double-stfingedVSA. Measurement Because the lunar value of g is approximately 163 000 regal and a measurement to the precision of 0.1 regal is desired, the difference frequency of the VSA must be measured to an accuracy of approximately 1 X 10 -6. Because the nominal values of the difference frequencies in the normal and inverted positions are approximately 28 and 14 Ha, respectively, a simple counting of the cycles obviously will take an impossibly long time. Instead, a gate is generated that is inversely proportional to the difference frequency. For the normal case, the gate consists of 1536 cycles of the difference frequency Af n (approximately 55 sec at this frequency); for the inverted case, the gate consists of 384 cycles of the difference frequency Af/(approximately 27 sec). The width of the gate is measured by counting the pulses from a precision 125-kHz clock by a counter. If D n and D i are the counts in the normal and inverted case A = fn 1536 x /25 x 103 = 1.92 x 108 O n On (13-5)

reduction in the values of the higher order terms. Even-order terms of the type kzg2 give rise to nonlinear rectification of inertial accelerations caused by vibrations; therefore, it is very important to keep the terms small, The constants ko, k_, ks, and k 3 are determined for the sensor before the mission. However, experience with sensors of this type had shown that k0 is subject to drift as well as tares (sudden dc shifts), Any shift of k o would degrade the Earth-Moon gravity tie. (Shifts in k_, ks, etc., are much less important.) Also, if, at a station during a traverse, a large difference of gravity from the value at the LM site was indicated, it would be necessary to inquire whether this was a real variation in gravity or whether tile value of k o had shifted. For this reason, provision was made to make independent determinations of k0 when necessary. Such a determination is called a bias determination and is made by inverting the instrument. In the inverted case

Afi = _k 0 + kl_7 - k292 + Lag _'_

(13-4)

By assuming the values of kl, ks, and k3, the values of k0 and g can be determined from the values of Af n and Af i by combining equations (13-3) and (13-4).

125 (13-6) Afi = 384 x D. x 103 = h.8 x 107 D. 7, * If k0, kl, k_, and k 3 are all known, equation (13-3) can be used to determine the value of g from Afn" If

13-4

APOLLO 17 PRELIMINARY SCIENCE REPORT the precision heaters. A tap from the demodulator output is converted to digital form and forms a digit of the TGE display. The displayed digit marks the deviations of the precision oven temperature from a preset value. The outer oven thermostat and heater circuit merely react to temperature changes to control the power supplied to a heater. A thermal blanket provides good thermal insulation for the TGE. A radiator at the top of the instrument provides the primary means of heat expulsion. The mode of operation of the instrument was such that the radiator was left closed during each EVA. The instrument electronics produced heat, but this heat merely reduced the heating to be done by the ovens. Between EVA periods, the instrument was placed in the shade with the radiator open, and heat was then expelled into space. The temperature monitors are the eighth and ninth digits of the TGE display. The eighth digit gives the thermal condition of the outer oven and the sign for the ninth digit. The ninth digit of the numerical display is a number from 0 to 7 that represents a deviation of the precision oven temperature from a set point of 0.005 K times the digit displayed. Polarity of the deviation is obtained from the value displayed in the eighth digit. Physical Description of the TGE

k0 is not assumed to be known, equations (13-3) and (13-4) together can be used to determine the value of g as well as k o from Afn and Af i. Leveling If the VSA axis is not vertical but is inclined at an angle 0 to the vertical, g cos 0 is measured instead of 0. For a small O, the error is 0.5g02. The TGE is designed to keep O less than 00003 ' Of arc and, consequently, the error caused by leveling less than 0.06 mgal. To provide the leveling, the sensor is mounted on a gimbaled frame. Two vertical pendulums mounted on the gimbal frame sense departures from the vertical through comparator circuits. These comparator circuits provide information to stepping motors that drive the gimbals until the pendulums are level. The leveling is accomplished in two modes. When a pendulum is more than 00032 ' of arc from level, the corresponding stepper motor slews faster; at less than 00032 ', /he motor slews at a slower rate to avoid overshoot. When the pendulums are within 00°03 t of arc of being level, the slew commands are disabled, When the instrument has to be inverted in the bias mode, a set of bias pendulums is used that gives signals unless the gimbal frame is similarly leveled in an inverted position. The TGE carl be leveled only if it is initially placed in a position less than 15 ° from level. In the normal mode, time for leveling is between 0 and 20 sec; in the bias mode, the time is between 90 and 130 sec. Temperature Control and Monitoring

The TGE consists of the instrument package, a battery pack assembly, a thermal blanket, and an isoframe assembly. A cutaway view of the TGE is shown in figure 13-3. Outer Structure.-The outer structure of the TGE is cylindrical with a flat rear surface. A folding handle at the top of the instrument is used for hand carrying and for latching the instrument to the isoframe assembly. Three feet at the base of the instrument enable lunar surface operations. A radiator at the top of the instrument provides the primary means of heat expulsion. The radiator and the display panel are protected from the environment by hinged insulating covers over each. Inner Structure. The inner structure of the TGE consists of a two-axis gimbal system, which contains a VSA housed in a thermally protected and evacuated two-stage oven assembly. The oven assembly is enclosed in an electronic frame (E-frame)assembly of similar structural design. The E-frame assembly is pivoted about its axis and supported by a middle

Because the VSA sensor is extremely sensitive to temperature, it is necessary to controlits temperature to within 0.01 K. The VSA and its oscillatoramplifiers are encased in a precision oven that is maintained at a temperature near 322 K to within 0.01 K by the temperature control and monitor circuit. The precision oven, in turn, is encased in an outer oven that protects the inner oven from the external thermal disturbance. The precision oven temperature circuit has propertional and rate control and uses an electrical heater and a resistance thermometer element for a sensor, The complete temperature sensor is an ac excited bridge, two arms of which are thermistors. The bridge output is demodulated and used to control drivers for

TRAVERSE GRAVIMETER EXPERIMENT Z Radiator_
Nandlp ', _ I

13-5

ass-e'm'bi[ ',,_'" .....

.--Cover(display andcontrol)

zmd ninth digits of the display are thermal monitors, as explained in the section entitled "Temperature Control and Monitoring." however,display stays on for any sec. The display can, The be turned on at 20 subsequent time by depressing the "READ" pushbutton, and it stays on ]'or 20 sec. A measurement with the sensor in the inverted position is made by depressing the "BIAS" pushbutton. The bias pendulums are used for leveling, and the indicator light flashes on and off until the sensor is leveled in an inverted position. The counting and display then proceed as for the normal measurement. To conserve power, a toggle switch is provided to .,;elect tire "STANDBY" or "ON" mode of operation. In the "STANDBY" mode, power is supplied only to the oven temperature controls and to the VSA oscillator-amplifiers. Cycling the switch from "ON" to "STANDBY" to "ON" will erase any stored data. Depressing the "READ" pushbutton after such a ,,;witching provides valid readings only for the eighth digit, which is the temperature monitor for the outer oven and f or the battery. RESULTS Number of Readings Of the 26 readings obtained (table 13-I), three

Gravimeter measurements were made both with the TGE mounted on the lunar roving vehicle (LRV) and with the TGE placed on the surface. During a measurement, the TGE must be placed on a surface such that the vertical axis of the TGE is within 15° of vertical. The TGE must not be disturbed for approxilately 3 min after a measurement has been initiated, A normal measurement (one with the _nsor in the normal, vertical position) is initiated by depressing the "GRAV" pushbutton on the TGE(fig. 13-3). The measurement cycle starts with leveling of the instrument. During the leveling cycle, the indicator light flashes off and on. When the instrument comes to a rest within 00003 ' of arc of the vertical, the light stops flashing and remains illuminated until the difference frequency of the strings has been measured. The number of counts of a precision clock (from which the frequency can be obtained) forms the first seven digits of the TGE display. The eighth

(readings 1, 10, and 18) were obtained to learn the thermal state of the instrument before the EVA periods. No gravity values were obtained with these readings. Reading 8 at the LM site showed that the TGE had been moved during the measurement as indicated by the phase lock loop alarm, which gives zeros in the first three digits of the display in such instances. This reading, therefore, was valueless, and another reading was obtained at the same site. At the LM site, nine readings were made. Six of these were readings in the normal TGE position (upright) on the lunar surface (readings 3, 9, 11, 17, 19, and 25); one reading was made at the start of each EVA and one at the end of each EVA. Two ieadings (4 and 26) were made in the inverted position to determine the value of the bias term k0 at the beginning and end of the measurements. One zeading (2) was made on the LRV to compare "on LRV" and "off LRV" measurements. Besides the readings at the LM site, 11 other

TRAVERSE GRAVIMETER EXPERIMENT discrete measurements were made at different sites (readings 5, 6, 7, 12, 13, 14, 15, 16, 20, 21, and 23). Two extra measurements (readings 22 and 24) were made at stations 8 and 9 on the lunar surface to compare on-LRVand off-LRV measurements at these sites, In the preliminary evaluation of gravity in table 13-I, the constants k z and k3 of equation (13-3) are igr_ored and a value of k_ = 0.0001318 Hz/mgal is assumed. For obtaining the value of gravity Ag at the stations relative to the value at the LM site, it can be shown that, when k_ and k 3 are ignored, an approximate value is given by _g = (Dn - Dn base) x (-0.032_5) (13-7)

13-7

report, the resultant banging of the pallet may have caused instrument problems resulting in an erroneous reading 25. All the remaining values were negative. Nevertheless, a consistent drift pattern was not detected; hence, a zero drift was adopted. The variation in values is attributed to instrument noise, which has an rms value of 1.8 mgal. Comparison of On-LRV Off-kRV Values and

Readings 2 and 3 were both obtained at the LM site. Reading 2 was taken with the gravimeter on the LRV, and reading 3 was taken with the gravimeter on the lunar surface. The difference between the two :ceadings was 4.6 mgal. In an effort to determine whether this difference was random or systematic, on-LRV and off-LRV readings also were taken at :stations 8 and 9. As shown in table 13-111, the lunar :surface readings are, in all three cases, lower than the LRV values (the free-air difference is negligible) by amounts ranging from 4.6 to 6.9 mgal. There is no explanation for this difference; however, on the basis of three readings, an empirical correction of- 6.0 regal has been made to all on-LRV measurements (table 13-I). Some support for this correction comes :also from postmission tests with the engineering and spare flight models. When the handle of the gravi:meter was jarred, temporary shifts in the gravimeter :measurements occurred that were always in the same direction (although these shifts were < 6 mgal). By applying the - 6.0-mgal correction to the value at the .Apollo lunar surface experiments package (ALSEP) site, this measurement is brought into agreement with the measurement at the LM site. The gravity values at the two sites are expected to be close. However, agreement between the value at the LM site and that at the nearby surface electrical properties (SEP) experiment correction. site deteriorates slightly as a result of this

where Dn is the display (first seven digits) at that station and Dn base is the display at the LM site. The first off-LRV reading at the LM site (3) was chosen as the Dn base" The values of z_g thus obtained are given in table 13-I. Gravimeter Drift

For the flight instrument, it was determined before the mission that the drift during the EVA period (--_7 hr) was essentially zero. Therefore, it was decided to adopt a zero drift rate unless the off-LRV values at the LM site showed a consistent drift pattern. The off-LRV values at the LM site are given in table 13-11.Relative to the first reading, the gravity values range from 2.1 to -3.2 mgal. The only positive value, 2.1 mgal, was reading 25. Before reading 25, during the traverse from station 9 to the LM site, the pallet on which the traverse gravimeter was mounted swung open, and, as noted later in the TABLE 13-II.-Off-LR V _g Values at LM Site Relatt've to First Value Obtained [rms deviation = 1.8 mgal] Reading 3 9 11 17 19 25 _g, regal 0.0 - 1.4 - .2 - 2.0 - 2.1 3.2

Earth-Moon

Gravity

Tie

On the basis of normal reading 3 and inverted reading 4 (table 13-IV), a value of g = 162 694.6 mgal was measured at the LM site at Taurus-Littrow. The constants k_, k2, and k3 used in this determination were obtained during preflight tests. The value of ko obtained as a result of readings 3 and 4 was 7.21591 ]-IZ.A predicted value of ko based on laboratory test data was 7.2144 Hz. The total shift during the

of k 0 and g at LM Site from Readings in Normal and lnverted Positions
I

Af n

192 X 108 Hz Dn EVA-1

Afi

4.8 X 107 Hz Di

] ko, Hz

L

g, mgal

3 4

Normal ] Inverted [

Dn =670 0172 Di = 337 4540

28.655981
EVA-3

14.224161

_ 7.215910

)

162 694.6

26 25

Inverted Normal

Di = 337 4171 Dn=6700107

28.65626

14.225716 -

} 7.215272

[ 162701.5

translunar phase was 0.0015 Hz. This corresponds to a bias shift of approximately 11 mgal, which is considered reasonable when compared to typical bias shifts experienced during acceptance and vibration testing. On the basis of normal reading 25 and inverted reading 26, a second value ofg = 162 701.5 mgal was determined after EVA-3. The value for the bias constant k0 differed by approximately 0.00064 Hz from the initial value, which implies a shift of approximately 5 mgal in the bias value. However, the normal measurement of gravity obtained for reading 25, if the initial value of k 0 is used, differs by only 2 mgal from the initial value. During the traverse from station 9 to the LM site, the pallet on which the traverse gravimeter was mounted apparently swung loose and banged against the LRV. This was the only time during the entire mission that the gravimeter was shocked in this manner. Because deterioration in the performance might have resulted from this shock,.less emphasis has been placed on readings 25 and 26 and

the initial determination of 162 694.6 mgal has been adopted. An uncertainty of +-5 mgal is ascribed to this measurement. DISCUSSION Computation of Bouguer Anomalies

For a preliminary interpretation of the gravity measurement, two-dimensionality is assumed. The problem then essentially is reduced to the determination of the substructure of the linear Taurus-Littrow valley with linear massifs on either side. The stations at which the gravity measuremerits were made are shown in figure 13-4;the values at these stations were projected to a roughly southwest-to-northeast cross section. The value at station 6 could not be appropriately projected to this cross section and has been ignored in the present discussion. The great structural relief of the area makes three-dimensional calculations necessary. Such calculations will be described in

TRAVERSE

GRAVIMETER

EXPERIMENT

13-9

21

? ] 4575 _ __ ("('-_-"_"-',__

//

o

5500"-3_f- k._

_"2000_

_

Station no. 5 r l "T"--_q r-

North Massif

•

b 4853. 5500v..f.._.,..., t,......_..f. 6555_ "_kf-_

_ 1000 _ 0 I' ,

i

f

i

t

Distance,km FIGUREprojected13-5.-Topographie profile showing locations of stations. Station I and the ALSEP and SEP sites have of theomitted becauseelevation datum (abscissa) is the that been LM site. The their elevations are the same as elevation of the LM site.

FIGURE 13-4.-Contour at which Taurus-Littrow landing were showing the stations map of gravity measurements site, 0ower the cutting trending northeast through to which the site is left) and plane for the cross section the landing gravity measurements were projected. (Based on operational topographic map starting near Littrow BD Crater made. The straight line prepared by U.S. Army Topegraphic Command, October 1972. Contour interval, 500 m.)

'_-15 _-20 'q -3(] -35 -4(3 _ -45 -25 -5(3 -55

./ _' / "_-- Free-air anomaly .... Observedanomaly

_

"'"

"x
N. I q

?_ I I i 2

I 3

I 4

I I I I 5 6 7 g Distance, km

I I I I 10 II 12 i_

a later report. The topographic locations of the projected stations 13-5.

profile with the is shown in figure

FIGURE 13-6.-Observed anomaly and free-air anomaly profiles across the Taurus-Littrow valley. 13-1). The elevation datum chosen was the elevation of the LM site (fig. 13-5), which was the lowest elevation on the profile. The Bouguer correction is, in effect, made in three parts to show the effect of (1) the valley floor (i.e., material lying between the elevation of the stations and the elevation datum; shown with a density ofp= in fig. 13-1), (2) the North Massif, and (3) the South N,lassif. The three Bouguer correction curves and the total Bouguer correction are shown in figure 13-7. Note that the effect of the valley floor tends to c_mcel the effect of the massifs; hence, the total Bouguer effect is quite small (< 5 mgal). The Bouguer correction was calculated using a density of 2.0 g/cm 3 (Pz = P_ = 2.0 g/cm3). This value is lower than the values for breccia densities shown in figure 13-8(a). However, if an average density of 2.5 g/cm 3 were used instead of 2.0 g/cm s , the difference in the

The observed anomaly z_g, as obtained in table 13-I, is plotted as a function of distance in figure 13-6. The observed anomaly is approximately 50 mgal lower at station 2, closest to the South Massif, and approximately 30 regal lower at station 8, closest to the North Massif, relative to the value of gravity at the LM site. The observed anomaly curw_ therefore shows a pronounced dip toward the massifs on either side. The free-air correction is applied by using the correction previously given, 2gm/r. The free-air anomaly thus obtained (also plotted in fig. 13-6) dips to approximately - 30 mgal near the South Massif and to 20 mgal near the North Massif relative to the value at the LM site. The Bouguer correction is applied next. In making the free-air correction, as well as the Bouguer correction, an elevation datum must be chosen (fig.

13-10 Stationno. t_ "_ 1000 2 2A 3 _ 4 0_ "' Valley floor' 10 4

APOLLO 17 PRELIMINARY SCIENCE REPORT not always indicated in the sources but, when given, was one of the following. 9 8 8 1. The volumes of aluminum foil models of the

ALSEP LM 5. ALSEP, ,t_M

whole rocks were measured, and the bulk densities were computed using the weights of the rocks. Because the aluminum foil models were not made to great accuracy, these density values can have percent or even greater errors. 10

2. The volumes of small, precisely shaped samples of the rocks were computed by measuring their linear dimensions. The small samples are generally parallelepipeds, 1 by 1 by 2 cm. The densities were then computed using the measured weights of the small samples. 3. The densities of some small samples were measured directly using Archimedes' principle. The density values tended to group on the basis of the method used to compute the density: the first method giving low values, the third method giving high values, and the second method giving values in the middle. This result is reasonable because the samples were generally vuggy, vesicular, porous, or highly fractured. Thus, the first method includes the effects of the largest rugs and vesicles and the third method includes only the effect of the unconnected pores and cracks; the second method will generally eliminate the effect of large vesicles and vugs but not th_at of small cracks and pores that cannot be avoided in cutting the small samples. Thus, an intrinsic density of approximately 3.4 g/cm 3 for the lunar basalts is indicated in figure 13-8(b). Porosities have been measured for a few samples by point counts on thin sections or cut surfaces. A plot of density as a function of porosity and the intrinsic densities calculated from the porosities is given in figure 13-10. The intrinsic densities range from 3.25 to 3.49 g/cm 3 for the three basalts and from 2.99 to 3.14 g/cm 3 for the five breccias. Figures 13-8(b) and 13-10 indicate that the bulk densities of mare basalt samples are determined by their porosity and that the samples have an intrinsic density of approximately 3.4 g/cm 3 . Thus, a thick, mare lava flow with a thin, vesicular top would have a bulk density somewhat less than 3.4 g/cm 3 . The data on the breccias are not as conclusive, but there is no evidence that the highly fractured rocks and breccias forming the highlands are more dense, on the average, than the average of the breccia samples thus far reported. Therefore, the density contrast between a

FIGURE 13-7.-Application of the Bouguer correction to determine the Bougner anomaly profile across the Taurus-Littrow valley, showing the effect of the valley floor, of the North Massif, and of the South Massifand the total Bouguer correction. The free-air anomaly curve (fig. 13-6) is included for comparison with the Bouguer anomaly curve,

computed total correction would, in all cases, be less than 1 mgal. That difference can be ignored for the present discussion, The resultant Bouguer anomaly curve, included in figure 13-9, shows minimums of near --25 regal at the stations closest to the massifs. The variation in the central part of the valley floor is within 10 mgal of the value at the LM site. This curve has to be interpreted in terms of the substructure of the valley, To do so, what is known about the densities of the lunar rocks must be considered first. Densities of Lunar Rocks

No particular effort has yet been made to measure the bulk densities of the returned lunar rock samples, However, a few measured density values have been reported in the literature (refs. 13-3 to 13-21). 5 Most of these values were obtained in the coursq of measuring other physical properties of the lunar rocks (e.g., seismic velocity, heat conductivity, etc.). These published values are plotted in the histograms in figures 13-8(a) (lunar breccias) and 13-8(b) (lunar basalts), The method used to obtain the density values was Also N. Warren,private communication, 1972, and G.D. O'Kelley, personal communication, 1973.

FIGURE 13-9.-Assumed model for subvalley densities to explain gravity anomalies, including the Bouguer anomaly curve. On the ordinate for the topographic profile, the elevation and depth are referenced to the elevation datum (0 m), which is the elevation of the LM site. The shaded rectangle represents a postulated block of basaltic material underlying the valley floor, where Ap is the positive density contrast with respect to brecciated highland material on either side. thick, mare basalt formation and highland breccia material should be at least 3.2 - 2.8 = 0.4 g/cm 3 and may be as much as 3.3 - 2.3 = 1.0 g/cm a . Structural Model

anomaly amplitude (from edge of valley to center of valley) as well as in the slope of the Bouguer anomaly curve near the edges. In this connection, the values obtained at stations 2A and 6 will be especially useful in refining the nature and position of the margin of the inferred high-density body underlying the valley floor.

From the results of the last section, a very simple model has been used to explain the gravity results. Assuming that the subvalley floor material consists of basalt flows that have a positive density contrast of 0.8 g/cm 3 with respect to brecciated highland material on either side, a thickness of 1 km is obtained for the block of basaltic material (fig. 13-9). The large Bouguer gradients at the valley edges indicate steep sides for the postulated block of basaltic material. The sides are not at the edges of the valley but lie approximately 1 km inside the edges of the valley, These are very preliminary conclusions based on the work performed to date. More elaborate models have not been presented because we expect that the three-dimensional terrain and Bouguer corrections wiU change the final Bouguer anomalies by 30 to 40 percent. These three-dimensional based on the newer topographic compiled. Changes are expected calculations will be maps currently being in the total Bouguer

SUMMARY

AND

CONCLUSIONS

The successful performance of the TGE indicated that the value of gravity at the Taurus-Littrow landing site is 162 694.6 + 5 mgal. The Bouguer anomaly, analyzed with a two-dimensional approximarion, shows values approximately 25 mgal lower at the edges of the valley than at the LM site• The Bouguer anomaly curve is interpreted in terms of a 1-km-thick block of basaltic material lying below the valley floor with a positive de.nsity contrast of 0.8 g/cm a with respect to the material on either side. R E F E R EN CES 13-1. Talwani, Manik; WorzeI, J. Lamar; Two-Dimensional Mark: Rapid Gravity Computations for and Landisman, Bodies with Application to the Mendocino Submarine Fracture Zone. J. Geophys. Res., vol. 64, no. 1, Jan. 1959, pp. 49-59.

The purpose of this experiment was to measure the variations in the lunar gravitational field near the trajectory of orbiting space vehicles (i.e., the command and service module (CSM) and the small particles and fields subsatellites ejected from the Apollo 15 and 16 spacecraft). New information has been obtained from all Apollo orbiting spacecraft; however, this report shall be limited to the results from the Apollo 17 CSM and the Apollo 16 subsatellite. The data acquisition technique and data reduction methods have been presented in previous reports (refs. 14-1 and 14-2) and will not be discussed in this report. The data acquired are precise speed measurements of the orbiting spacecraft from which accelerations or gravity prof'des may be inferred. Feature resolution is controlled by the spacecraft altitude and is almost a direct relationship (i.e., data taken from a 50-km altitude will resolve approximately a 50-kin feature). Therefore, revolutions 3 to 12, when the CSM was in the low-altitude orbits, provided the clearest information, The characteristics of the Apollo 17 CSM and the Apollo 15 CSM orbits were very similar. Consequently, some of the larger lunar features were traversed by both vehicles, permitting a broadening of the detailed investigation of the Serenitatis, Imbrium, and Crisium mascons. At present, one gravity profile has been reduced. The surface track of that profile and an Apollo 15 track are shown in figure 14-1. The corresponding gravity profile is shown in figure 14-2. These are line-of-sight accelerations (i.e., accelerations projected along the Earth-Moon line) and have no corrections applied for altitude or viewing geometry, The pronounced features are again Mare Serenitatis and Mare Crisium; however, additional features are identifiable.

PRELIMINARY

RESULTS

A large negative gravity region x between the Serenitatis and Crisium mascons is located very near the Apollo 17 landing site (long. 30 ° E, fig. 14-2). Lrsing this anomaly with a 43-percent increase attributable to least-squares f'dtering (ref. 14-3) and with the best estimate of the landing site lunar radius (1734.5 km), an absolute gravity estimate of 162 722 regal is obtained. This estimate compares favorably with the traverse gravimeter result of 162 694 mgal (see. 13) and instills additional confidence in the remote-sensing results. The difference of 28 mgal could be accounted for by the altitude difference, because our result was obtained at spacecraft altitude (15 km) rather than at the surface, or by small local anomalies of this order as measured by the traverse gravimeter (see. 13). Farther west on the figure 14-2 profile, the Mare Vaporum region (long. 3° E) is a negative anomaly. A stronger negative anomaly at longitude 4.5 ° W is over part of Montes Aperminus and between two ridge formations. At longitude 10° W, the edge of the Sinus Aestuum mascon was sampled. The small negative anomaly at longitude 20 ° W is produced by the crater Copernicus. The other anomalies across Oceanus Procellarum do not seem to correlate well with any _isible surface features; however, they do correlate perfectly with previous work (refs. 14-4 and 14-5). "['he 50-mgal high at longitude 66 ° W is produced by Grimaldi (peak displaced because of geometric effi;ct). When data from all 10 revolutions (3 to 12) are reduced, there will be 10 east-west Grimaldi profiles evenly spaced from the northern to the southern edge. Some of the most obvious points concerning the 1A negative gravity region, often referred to as a negative anomaly, is def'med as a region havinga massdeficiency with respect to a homogeneous sphexiealbody. A corresponding definition applies to a positive gravity region (or positive anomaly),sometimes called a gravity high.

FIGURE 14-1.-Surface tracks of the Apollo 15 CSM during revolution 4 and of the Apollo 17 CSM during revolution 5.

100[_' 50F^ =" 0_/e \

_ _ I -50

/e_

_v_,v

A __]_t _f

mascon prof'des are that (1) the Serenitatis profile from the Apollo 17 data has ahnost the same maximum acceleration as the Apollo 15 profile (fig. (2) the western shoulder seen in the Apollo 15 profile 14-3) even though it is more than 200 km off center, of Serenitatis is not seen in the Apollo 17 profile, and (3) the Crisinm profiles from the Apollo 15 and 17 data are very similar and cover approximately the same region (figs. 14-1 and 14:4). A theoretical gravity profile for Apollo 17 revolution 5 was generated using the best model of Serenitatis developed from Lunar Orbiter V and Apollo 15 data. The comparison of the actual and theoretical curves is shown in figure 14-3. There is approximately a 40-percent error from the actual observations, showLugthat new information can be extracted from these data. The same comparison is shown in figure 14-4 for the Crisium mascon, but the differences are relatively small. The Grimaldi anomaly was analyzed using a surface disk model in which the mass, the radius of the disk, and the longitude of the disk center were estimated simultaneously. Doppler data were gencrated with this model and reduced in precisely the same manner as the actual observations. Several

FIGURE 14-5.-Contou_ map of gravity from longitude 30° to -30 ° based on line-of-sight acceleration data from the Apolgo 16 subsateUite. (Contour units are in miBigals.)

iterations using a least-squares criterion on the acceleration profile yielded a mass of 1.013 × 10 _0 g and a radius of 70 km at -68 ° longitude. (Latitude was held at -5.50°.) The mass distribution from this restdt yields 1000 kg/cm 2 , which is 25 percent higher than that determined for the other mascons. These very preliminary results may change when all profiles are analyzed together, The Apollo 16 subsatellite at an orbitalinclination of 9.5 ° provided new high-resolution observations over a region from latitude 9.5 ° N to 4 ° S and from longitude 70 ° E to 70 ° W. The altitude was approximately 20 km at latitude 6 ° N, 40 km at latitude 3 o N, and 60 km at latitude 4 ° S. The data were acquired during 68 revolutions, which provided highly redundant coverage. The acceleration profi!es from these revolutions have been contoured and superimposed on lunar charts. Only the central

section from longitude 30 ° W to 30 ° E is shown in figure 14-5 because that section contains most of the new features. A more detailed presentation is given in reference 14-5. The outstanding features are as follows. I. The negative anomaly centered in Copernicus, which is another example of an unftlled crater having a negative anomaly 2. The positive anomaly just southeast of Copernicus that does not coincide with a visible s'_rface feature but may be correlated with a large, ancient ring structure south of Imbrium (as shown in ref. 14-6) 3. The Aestuum positive anomaly that was det(;cted in the original mascon mapping (ref. 14-7) 4. The gravity high at longitude -6 ° , latitude 4 ° 5. The Sinus Medii gravity high

14-4

APOLLO

17 PRELIMINARY

SCIENCE

REPORT

6. The Triesnecker positive anomaly centered over the dense rille formation just north of the main crater 7. The Lamont positive anomaly in Mare TranquiUitatis centered over the flooded crater and wrinkle-ridge structure The last two positive anomalies seem to be associated with rille and wrinkle-ridge features that are often referred to as volcanic examples. They are also the first strong positive anomalies over mafia terrain are not correlated with ringed basins. that

CONCLUSIONS
The Apollo 17 data will provide a more detailed determination of the Serenitatis mascon, because it is clearly evident that the present model is inadequate. Grimaldi has a mass distribution larger than other mascon distributions, but this very preliminary result may change and show better agreement. The Apollo 16 subsatellite data reveal high gravity regions over mare areas not associated with ringed basins but over formations of probable volcanic origin (refs. 14-8 to 14-10). A positive anomaly southeast of Copernicus does not correlate with any visible feature and may be part of an ancient ringed structure that is almost obliterated.

ACKNOWLE DGM ENTS
The authors thank A. O. Kiesow of the Jet Propulsion Laboratory and H. Moore and J. Slater of TRW/Houston for

The surface electrical properties (SEP) experiment was used to explore the subsurface material of the Apollo 17 landing site by means of electromagnetic radiation. The experiment was designed to detect electrical layering, discrete scattering bodies, and the possible presence of water. From the analysis of the data, it was expected that values of the electrical properties (dielectric constant and loss tangent) of lunar material in situ would be obtained, The SEP experiment is important for several reasons. First, the values of the electrical properties of the outer few kilometers of rock and soil of the Moon, measured in situ for the first time, may help others interpret many observations already made with both Earth-based and lunar orbital bistatic radar, Second, the SEP experiment will provide data that are needed to interpret the observation.,; made with the lunar sounder, an Apollo 17 orbital experiment. In the Apollo lunar sounder experiment, the time intervals required for electromagnetic waves to penetrate the Moon, be reflected, and return to the surface of the Moon were measured. Of more interest than times, however, are depths, which can be obtained from the lunar sounder delay times and the dielectric constant that is measured in the SEP experiment. Third, the results of the SEP experiment are expected to help define the stratigraphy of the Apollo 17 landing site. Visual observations made by the crewmen and recorded with cameras are restricted aMassachusettsInstitute of Technology. bNASA Lyndon B. Johnson Space Center. CUniversityof Toronto. dRaytheon Company. eU.S. GeologicalSurvey. J'PrincipalInvestigator. :_ Coinvestigator. 15-1 .

to the surface of the Moon. The SEP experiment will extend to depth those visual observations made at the surface and perhaps reveal features at depth that do not reach the surface. DESCRIPTION OF THE EXPERIMENT

The basic principle of the SEP experiment is interferometry. This principle involves only the interterence of two or more waves to produce an interference pattern. The inversion of the interference pattern in terms of the spatial distribution of the electrical properties is the basic aim of the experiment (fig. 15-1). The experiment is most easily understood in terms of a single dipole antenna for radiating electromagnetic energy and a loop receiver for measuring the magnitudes of the fields. In the

Receiver /, ,,Transmitter Receiving antenna, t "_" ,_r"_._

.Transmittingntenna a Lunarsurface. " Path1 Lunarroving vehicle

_ i

_FtGURE 15-1.-Simplified schematic diagram of the SEP experiment. Electromagnetic radiation from the transmitting dipole antenna travels along path 1 (above the surface), along path 2 (below the surface), and, if reflectors are present, along path 3.

15-2

APOLLO

17 PRELIMINARY

SCIENCE

REPORT

early developmental stages of this experiment, exactly this configuration was used (ref. 15-1). The electromagnetic energy radiated from the transmitting antenna travels along various paths. In the "half-space" case, one wave travels above the interface through "free" space and another travels below the interface through subsurface material, Because the velocity of electromagnetic waves in a solid medium is different from that in free space, the two waves interfere and produce a distinctive interference pattern. This case has been studied extensively from both experimental and theoretical viewpoints since 1909 (ref. 15-2). The correct mathematical solutions, although somewhat complicated, are now well known (ref. 15-3). An example of a theoretical interference pattern for the half-space case is shown in figure 15-2. The spacing between successive maximums or successive minimums is related to the frequency of the wave and to the dielectric constant

of the medium, and the rate at which the field strength decreases with distance is related to the loss tangent of the medium. This type of pattern is present in some of the lunar data. If a reflecting horizon occurs at depth, such as the case shown schematically in figure 15-1, then a reflected wave will interfere at the surface of the medium with the other waves. Figure 15-3 is a theoretical curve showing the distinct interference pattern produced by a reflected wave. The presence of additional reflecting horizons in the subsurface would produce still more complicated interference patterns. In the Apollo 17 SEP experiment, two crossed dipole antennas that radiated sequentially were used. In addition, several frequencies-l, 2.1, 4, 8.1, 16, and 32.1 MHz-were used. Because each transmitting antenna radiates at each frequency for a sufficiently long time, the experiment results can be analyzed in terms of continuous waves. The shortest sampling time at the lowest frequency includes approximately 33 000 cycles.

The SEP experiment is the first geophysical field technique to use the dielectric properties of rocks rather than the conductive properties. In that sense, the experiment is entirely new. Consequently, all the

-_ E

0.56 .48 .40 .32 t,, ,24 .16 .08 I 2.50 I 7.50 I I I I I 10.00 12.50 15.00 17.50 20.00

Distance,free-spacewavelengths FIGURE 15-3.-Theoretical curve for the case of a single layer over a reflector. The layer is four free-space wavelengths (4h 0) thick (ref. 15-8).

SURFACE ELECTRICAL PROPERTIES EXPERIMENT experimental techniques and most of tile theoretical basis have been developed specifically :for the lunar experiment. Descriptions of the early versions (circa 1968) of the technique are given in references 15-1, 15-4, and 15-5. In this report, the physical and mathematical basis of the experiment is outlined and the discussions in references 15-6 to 15-8 are followed. Theoretical work has been limited to the electric and magnetic fields that result from dipole antennas on plane, horizontal, layered media. For mathematical details, the reader is referred to the original sources, In the theoretical development, consideration is

15-3

a is the attenuation constant. A typical component of electric field E at a large distance R from the radiating source varies with R according to E
= E0e-Jk'R =

given first to electromagnetic propagation in an unbounded, homogeneous, isotropic dissipative reedium and next to propagation near the plane interface of two semi-infinite homogeneous media (specialized to a lossy dielectric below an empty (or free) space region, popularly called the half-space case). Then, the effects ofinhomogeneous horizontal stratification are considered, specialized initially to a lossy dielectric region of two layers, the first of depth d and the second of infinite depth and having electrical properties differing from the adjacent layer and the semi-infinite space above.

(15-3)

(15-4)

The evaluation of the complex radical may be accomplished by the 50-yr-old method of G. W. Pierce (ref. 15-14), recently revived by King (ref. 15-9), as follows. -- f(P) - ga(P) 05-5)

UNBOUNDED, HOMOGENEOUS, I_OSSY
DIELECTRIC MEDIA where

pative media is treated adequatelyin in references dissiElectromagnetic propagation unbounded 15-3 fields with time t is usually expressed as exp(]'¢ot) and 15-9 to 15-13. Variation of electric and magnetic where the rotative operator/" = x/Z1 and the radian frequency ¢o = 27rf (where the frequency f is expressed in hertz); this exponential is hereafter suppressed. Meter-kilogram-second unffs are used where, in vacuo, the dielectric constant or permittivity eo = 1 × 10--9/367r F/m and the permeability 12o= 4zr X 10 -7 H/m. The phase velocity in vacuo is c = 1[Vx/V--_oe0 3 × 108 m/sec. Mathematically, the = field expressions are solutions to Maxwell's equations. The dissipative medium is characterized by its electrical constants, real relative dielectric constant er and conductivity a (mho/m). (For a vacuum, er = 1.) The media are customarily considered to be nonmagnetic with permeability/a =/a 0 . The finite value of a gives rise to a complex relative dielectric constant e'r, a complex refractive index N, and a complex phase constant k =/_ -/c_ where 13 the phase constant and is

where the function F(_,) is devoid of exponential behavior, H i is the zero-order Hankel function of the first kind, and 7i = ( x2 - k_) 1A may be called a complex propagation factor (i = 1 denoting the lunar soil and i = 2 the space above). The variable X used in equations (15-9) and (15-10) is a complex separation (or eigen) variable of integration and should not be confused with the wavelength. In a cylindrical coordinate system with the source dipole at a height h above the origin of the coordinates (p, q_,z), two essential integrals U(a,b,r) and V(a,b,r) are required to determine the vector potential II from which the fields E and H are derived. The relationship of E and H is derived from Maxwell's equations and continuity relations at the space-dielectric plane boundary (z = 0). The Uand V integrals differ in the value ofF(X) used; thus, for the Vintegral - k2¥ k_¥2 2 1 ,xz ,\ k_2)_x2k_)

d_B/lun = 1.64 _r' and a is independent of frequency. If o and er are constant with frequency, then p is proportional to f; if p is constant with f, then o/e r is proportional to f. Propagation in Layered Media

For propagation in semi-infinite space near and above a semi-infinite, homogeneous (nonlayered) lossy dielectric, see references 15-3, 15-9, 15-10, and 15-15 to 15-17. References 15-16 and 15-17 are especially useful for layered media. Earlier application was to ground-wave propagation along the surface of the Earth, generally where the loss tangent of the Earth is large. The mathematical solutions are involved; they were solved initially by Sommerfeld in 1909 (ref. 15-2) with later (1926) correction of the famous _ sign error (ref. 15-18). A complete history, with proof of the existence of Sommerfeld's controversial surface wave, is given by Bafios (ref. 15-3). The resulting field equations (for electric field E and magnetic field H) depend on the nature of the source. In theory, there are four source dipoles: the horizontal electric dipole (HED) and vertical electric dipole (wires), the horizontal magnetic dipole, and the vertical magnetic dipole (VIVID). In the SEP experiment, a tuned series of wire antenna radiators (thus extensions of the elemental HED) is used, and the cylindrical coordinate values of magnetic field Hp, H¢, and Hz are measured. The major difference in typical ground-wave propagation from that on the Moon (or in earthbound glaciers and deserts) is in the low values of er and p for the latter. For the case of a semi-infinite Moon below semi-infinite space, the solution is that for the

F(X) = l. _k_where
k2 k2 0 =

(15-10)

1 N2 + 3. ki
[30

(15-11) , _--_

k1 N .....
k 2

In equation (15-11), the refractive index N (eq. (15-4)) is the reciprocal of n used by Bafios (ref. 15-3) and others. For evaluating a component of the magnetic field (e.g., Ha) in the SEP experiment, the U integral is required (actually the partial derivative of U). Here, a = 0, b = h + z, and the exponential involving a in equation (15-9) is unity; thus, U is written as U(O,b,r). Ifh = 0, then Ubecomes U(O,z,r). The integral solution involves, generally, saddle-

SURFACE ELECTRICAL PROPERTIES EXPERIMENT point or double-saddle-point approximation methods (ref. 15-3). However, if h = z = 0, the solution for U(O,O,r) is exact, as found by Van der Pol. Thus, the expressions for Hz waves broadside to the horizontal wire (HED) are exact as are those for the tangential component of electric field E, (VIVID)(first noted by Wait (ref. 15-16)). If h or z (or both) are nonzero values, approximate methods must be used; these methods are very laborious because complex contour integration must be used with consequent studies of poles and branch cuts in the integrals l(a,b,r), The resulting field expression for the half-space case consists of two components, one a wave traveling above the surface with the phase velocity of space and the second a lateral wave; these two waves irlterfere. An example is shown in figure 15-2 for Hz lateral waves broadside to an HED for several values of erl and p! = 0.03. The lateral wave is that component of energy traveling in the dielectric but refracting across the boundary to reach the receiver at height h = z. For typical terrestrial soils, the loss tangent p of the ground is so high that the lateral wave is relatively too small to be observed. However, in glaciers, polar regions, and deserts, such interference patterns as those shown in figure 15-3 may be observed, Horizontal Stratification

15-5

integrals, similar to equation (15-9). The theoretical problem is reduced to that of solving the integrals. Three techniques have been used: (1) numerical integration on a digital computer, (2) asymptotic expansions that lead to geometrical optics approximations, and (3) contour integration to yield a normal mode solution (mode). In the geometrical optics approximation (GOA) method, the resulting field at the receiver consists of the space and lateral wave components (the half-space case) plus those attributable to reflections from the boundary between the upper layer of thickness d and the lower semi-infmite layer. (Lateral waves at this boundary and their effects have been generally neglected.) The formulation of reflections is approximate, but the GOA solution is considered satisfactory if the depth d is greater than the wavelength X in the upper layer. An example is shown in figure 15-3, where d = 4X0, for lateral waves broadside to an HED. In the mode approach, the contributions to the integrals are identified in terms of the normal modes of wave propagation. Multiple Layers.-Solutions to the various integrals (eq. (15-9)) for multiple layers can also be obtained by numerical integration and by using normal mode theory. The numerical integration method (refs. 15-8 and 15-19) provides quite exact solutions but requires much computer time; however, the method provides a check on other techniques and can be extended readily to large numbers of layers. In the GOA method, the problem is treated in terms or rays (thus, distances must be large compared with various wavelengths); therefore, solutions that are readily interpretable against a background of physical optics are provided. Unfortunately, the GOA is invalid for "thin"layers, thecase for both glaciers and the Moon for at least some of the SEP experiment frequencies. The formulation and solutions for certain parameters are given in references 15-6 and 15-8. The theoretical curve for one set of parameters is shown in figure 15-5. The lack of agreement between the GOA and the numerical integration at distances less than 7_ is caused by the approximations in the GOA and indicates clearly that the proper solution must be chosen for a particular experimental situation. The normal mode solution, valid for thin layers such as appear to be present at the Apollo 17 site, was formulated by Tsang, Kong, and Simmons (ref. 15-8). We are rather sure that our various formulations of the solution are[ correct. These formulations have

Two Layers.-Wave propagation in stratified regions has been treated generally by Brekhovskikh (ref. 15-17) and Walt (ref. 15-16); the properties of antennas in such regions have been discussed by Galejs (ref. 15-15). As specified for the SEP experiment, the previously mentioned treatments in references 15-6 and 15-8 find useful application. The geometry is that of figure 15-4. The solutions are Z l_ Medium 1
Medium 2

.2 •1 Distance, wavelengths _ .8.7 Z)C¢" "_ '_'_,_-,_ f" FIGURE 15-5.-Comparison of the geometrical optics approximation (dashed curve) with the Tsang exact solution (solid curve), obtained by numerical integration, for a single-layer case (ref. 15-8). Note the excellent agreement for all peaks except the f'ust. been tested against which the geometry gations using such field data collected on glaciers for was known from previous investiother techniques as seismic, gravCritical \\ I

k.,# ,ioadside pattern (a)

__3_.2

ity, and drilling (refs. 15-1, 15-8, and 15-20). They have also been tested against laboratory data obtained with analog scale models• The antenna radiation patterns of both the receiv-

ing loops and the transmitting dipoles are important in the analysis of the lunar data. The theoretical patterns for the transmitting antenna have been calculated (ref. 15-21), and the results are shown in figure 15-6. It has not been possible to calculate, with equal confidence, the patterns for the receiving antennas because of the effects of the lunar roving vehicle (LRV). From the data obtained on tile Moon, however, it is deduced that the influence on the H z component is minimal; thus, our preliminary data analysis is based on that component. In order to interpret the Hp and H¢_ components, the effect of the radiation pattern of the receiving antenna must be removed, THE EQUIPMENT Description On the Moon, the crewmen deployed a small, low-power transmitter (fig. 1.5-7) and laid on the surface two crossed dipole antennas that were 70 m long tip to tip. The receiver and receiving antennas, shown in figure 15-8, were mounted on the LRV. Inside the receiver, there was a tape recorder which recorded the data on magnetic tape. The entire tape recorder, the data storage electronics assembly (DSEA), was returned to Earth. In addition to the Tile electromagnetic radiation at the six SEP experiment frequencies is transmitted and received according to the scheme shown in figure 15-9. One data frame, which is 38.4 sec in duration, consists of six 6.4-sec subframes that are identical except for the receiver calibration and synchronization process. In subframe 1, for example, the receiver is calibrated at 32.1 and 16 MHz and the synchronization signal is FIGURE 15-6.-Model of the theoretical radiation pattern for the SEP experiment transmitting antenna on the Moon (ref. 15-22). (a) Diagram. (b) Photograph.

SEP experiment data, information on the location of the LRV, obtained from the LRV navigation system, was also recorded on the tape.

SURFACE
I

ELECTRICAL

PROPERTIES

EXPERIMENT

15-7

FIGURE 15-7.-The SEP experiment transmitter shown with the solar panel power source and dipole antennas dethe bottom five sides with a thermal blanket. Because the top of the unit is shaded by the solar panel, the uncovered surface needs only a coat of thermal paint to provide adequate cooling for the enclosed electronics. The balance between heat lost to electronics package is and on ployed. The transmitter cold space by radiationcoveredthat generated inside the unit by the electronics equipment is

° _) __ _'_

_)

and received on the X antenna. In dipole 2, the transmitted on the north-south (N-S)subframe antenna receiver is calibrated at 8.1 and 4 MHz and the very delicate synchronization and requires transmitted ondesign. signal is careful thermal the east-west (E-W) antenna and received on the Y antenna. Each experiment frequency sequence is repeated exactly as
shown in all six subframes. Each experiment fre-

_i _,__-_ '_L_-:._._
;-_ "'_-": ?4-

' _.
_':._

FIGURE 15-8.-The SEP experiment receiver and antennas. The receiver electronics, including tape recorder and
battery, are contained in the box (23 em_), which usually

quency is transmitted first on the N-S antenna for 100 msec and then on the E-W antenna for 100 msec.
During each 100-msec transmission interval, the

is completely enclosed in a thermal blanket. The thermal
blanket has been opened to show optical surface reflectots. The three-loop antenna assembly, folded during the journey to the Moon, is shown unfolded as it was used on

receiver "looks" at the transmitted signal for a period of 33 msec with each of the three orthogonal (X,Y,Z) receiving loops. In addition to the preceding operafions, once each subframe, the receiver observes environmental noise and records its amplitude,

the Moon. The receiver acquires the transmitter signal sequence automatically as long as the signal exceeds a given threshold. Synchronization of the receiver is

15-8

APOLLO 17 PRELIMINARY SCIENCE REPORT Such functions as signal synchronization, frequency mixing, and antenna switching are controlled by the timing section, which is, in turn, crystal controlled for stability. The entire receiver assembly is battery powered using primary cells and is enclosed, except for the antenna assembly, in a thermal blanket. The thermal blanket has two flaps that may be opened to expose optical surface reflectors, which form a thermal radiator for internally produced heat while reflecting heat from the Sun, to control the internal SEP experiment the receiver. The temperature of transmitter (figs. 15-7 and

designed to provide a minimum output of 10.0 W at 15-1t) and powered at 5 solar Like the receiver, the 15 V is 1.10 W by V. cell panels that are transmitter Also, separate stable crystal oscillators timing sequence is crystal controlled for stability. generate the signals that are radiated by the dipole antennas placed on the lunar surface. Because the antennas are required to radiate energy at six different frequencies, they are constructed in sections (fig. 15-12), and each section is electrically separated by electrical f'dters (signal traps). Each section of the antenna is of the proper electrical length for optimum performance. The dipole antennas, each 70 m long (tip to tip), are made of insulated wire between signal traps and were stored on reels until deployed. Performance on the Lunar Surface The crewmen deployed the SEP experiment equipment during the first period of extravehicular activity (EVA-l). Photographs of the receiver and of the transmitter and the transmitting antenna are shown in figures 15-13 and 15-14, respectively. Stereographie photographs will be used to obtain the location of the starting point of the SEP experiment profiles to within 1 m. The LRV, with its navigation system, was used to mark straight, orthogonal lines to be used as guides for deploying the antenna. Especially important for the analysis of the data was the fact that the arms of the transmitting antenna were laid out straight and at tight angles to each other. The SEP experiment operations were nominal during EVA-1. During the rest period between EVA-1 and EVA-2, however, the temperature of the SEP experiment receiver increased; subsequent overheating hampered the SEP experiment operation until the DSEA recorder was removed in the middle of EVA-3 to prevent loss of data that had been recorded already

_
[

16 ] 32.1 ] 8.1 [ 2.1 [ 16 [ 32.1 [ l
] [ [ [ [ [

}_ SF-I

1.6see Ca"_rat-r_Ssu"_/'ra-_'s SF-2 SF-3 SF-4 SF-5

[ N-S ] I0 2sync [ReceiveR[ End '1 SF-6

Cal32.1/16Cal8.1/4 Cal2.111Cal 2.1/16Cal8.1/4 Cal2.1/1 3 Sync N-S Sync -WSync -S Sync E N E-W Sync -S Sync -W N E ReceiveX ReceiveY eceveZReceiveX R ReceiveY ReceiveZ 64 , , ._ "--_ Data frame I 38.4sec ,= FIGURE 15-9.-The SEP experiment data format. The basic cycle, shown in the center of the diagram,starts with the 16-MHz signal and ends with the synchronization (sync) frame in the lower right corner. The cycle is 6.4 see long. (Values are frequenciesin megahertz.) The upper part of the figure shows a typical "data" frame. However, the singlecalibration (cal) frame changessuccessivelythrough the subframe (SF) sequence shown at the bottom of the diagram, accomplished when both (or either of) the 1- and 2.1-MHz signals exceed a given threshold. A block diagram of the SEP experiment receiver is shown in figure 15-10. The loop antennas are connected sequentially to a low-noise amplifier section, which amplifies, converts (in frequency), and logarithmically compresses the amplitude of the received signal. A constant amplirude, variable frequency signal (in the band 300 to 3000 Hz) corresponding to the logarithm of the received signal amplitude was recorded on magnetic tape in the DSEA. The DSEA can record nearly 10 hr of data. Upon completion of the experiment, the DSEA was removed from the receiver for return to Earth.

Oscillator/timing odule m Frequency generator I 1-MHzosc H Attenuator [------Attenuator • _ t I I I I I

- "-Dr-iver%m--pli'-fier-m_uTe-'] "-Ant_n_a464745

[
I

2.1-MHzosc

H
J_

'
/
I_[. " I I_i;.-, _____ I I ;-:! =- =amplifier J Driver Driver

J
4.0-MHzosc J_ Attenuator _. Summer and divider I I I I I

,
I I I I I i I I I I I I I

I
N-S I E-W I I

',
I 32.1-MHz oscH Attenuator_--_
I I r _

L. ....

i t

I

I

1.04-MHz 1=_7_ I

Timer "7 sequencer I

_

+5 V

cock I

l'"'ll;l___T.i._m_e[__E_E
J i I _u_n____l_
L t-t -- -- "t-t J

Solar
panel regulator) (including _
I-. ...............

...............

TO oscillators

To To N-S E-W drivers drivers
................................

+15V

FIGURE 15-11.-Block

diagram of the SEP experiment transmitter. the SEP experiment transmitter in 100-m increments, and the computed bearing to the SEP experiment transmitter in 1° increments. The navigational data are approximate because of wheel slippage on the lunar surface and will be improved greatly by including additional data on the LRV location obtained from photographs, crew comments, and longbaseline interferometry. The second kind of data, the primary SEP experiment data, consists of the three orthogonal magnetic components Hz, Hp, and He_, recorded as a function of frequency and of transmitting antenna (N-S or E-W). An example of the field strength data is shown in figure 15-15. The third kind of data, temperature experiment receiver, was obtained for of the SEP use in the

on the magnetic tape. The receiver contained a thermometer that was monitored by the crewmen, Despite the efforts of the crewmen to control the temperature, the receiver became too hot and was tumed offbyathermallyoperatedswitch, Data were obtained during EVA-2 on the traverses from the SEP experiment site toward station 2 and from station 4 toward the SEP experiment site. Data were not obtained during the early part of EVA-3 because the receiver switch was in the "standby" position rather than "operate." Apparently, the transmitter operated nominally throughout the mission,

THE Three kinds of data

DATA were recorded in the SEP

experiment: navigational data, electromagnetic field strengths, and the internal temperature of the receiver. The navigational data, obtained from the LRV navigation increments system, included odometer pulses at 0.5-m from two wheels, the computed range to

postflight analysis of the experiment. Because of the sensitivity of all magnetic tape to temperature, the potential loss of data from excessive temperature in the SEP Although experiment protection receiver against had been anticipated. overheating had been

FIGURE 15-12.-Electrical schematic diagram of the SEP experiment transmitting antenna. Only one-half is shown because the antenna is symmetric about the midpoint (A', A). Total physical length (tip to tip) of each section of the antenna used for each SEP experiment frequency is 2, 4, 8, 32, and 70 m. The symbol Z represents impedance, and the components labeled F 1 to F 4 are filters. 70

The analysis of each individual component at each frequency for each of the transmitting antenna orientations is quite straightforward. However, a FIGURE 15-14.-The SEP experiment transmitter and antenna deployed at the Apollo 17 site (AS17-141-21517). single model that perhaps because fits all the data has not been found, of the limitations of our present

theoretical development. For rigorous solutions, we are limited to models with homogeneous layers bounded by plane, horizontal surfaces. However, even within the limitations of our present theory, values of the properties of the lunar material in situ have been estimated , and some interesting conclusions electrical structure of the Taurus-Littrow been obtained, about the site have

near the surface to approximately 5 at a depth of 50 to 60 m. A discontinuity is present at 50 to 60 m, where er increases to a value of 6 to 6.5. Because no reflection appears to be present in the 1-MHz data, we expect that er does not increase between 60 m and at least 2.5 km. Compared to terrestrial values, the loss tangent is quite low (approximately 0.003) at all SEP experiment frequencies. On the basis of this low value of the loss tangent, we infer that water is probably not present at the Apollo 17 site. In the alternate structural model, the cause of the apparent assigned change of dielectric constant with depth is to a sloping interface between a thin upper

The discussion in this report is based mainly on the analysis of Hz, the vertical component of the magnetic field, for two reasons. First, although the radiation patterns of the receiving antennas have not been measured, distorted than it is expected those of the that the H z data are less other two components,

Second, the appearance of the H z data resembles more closely the glacier data, which comprise our background data. Two quite different structural models of the Apollo 17 site have been developed to account for the observations. Although neither is based on rigorous theory, we believe that each is correct in the essential members features. of the The first model, SEP experiment preferred team, by most is one in

layer with er = 3 to er = 4 and p < 0.04 and a thick lower layer with er = 6.5 and p = 0.04. Rigorous theoretical expressions have not yet been obtained for this case either. However, we have confidence in the general effects attributed to a sloping interface because of the following limiting cases of horizontal interfaces. 1. For interference a very thin layer (thickness < 0.1X), the of a half

pattern

is equivalent

to that

which the dielectric constant increases with depth, Each of the lunar profiles can be matched quite well with the theoretical curves based on a single layer. The parameters for each of these six single-layer models are shown in table 15-I, and a typical example of the match between the theoretical and observed curves is shown in figure 15-15. The composite these several models is shown in figure 15-17. of We

space in which er and p have the values of the lower layer (fig. 15-18, upper curve). 2. For a layer with thickness between 0.1X and 0.3X, the individual "wiggles" of the interference pattern disappear (fig. 15-18, intermediate curves). 3. For a layer with thickness greater than approximately 0.3X, the usual "reflected" wave appears in the pattern. The sensitivity of the interference pattern of a thin

believe that the H z data indicate that the dielectric constant increases with depth from a value of 2.5 to 3

SURFACE

ELECTRICAL

PROPERTIES

EXPERIMENT

15-13

5

10

.-f !i.

Max • - 15.505 "1"3"0000

20
E

ii

Max. -i,

"1"..0000

Max - -18.460 ._ _rI = 5.(]000

50
0 100 2 4 6 8 l0 12 14 Range, wavelengths 16

Max• -19.504 -6.0000 18 20 22

200

FIGURE 15-18.-Theoretical curves for thin layers, where Pl = 0.0300, er = 3.000, P2 = 0.0400, and er 2 = 6.000. • . , The points on _ae ordinate indicate the maximum values of each wave pattern. These plots are based on correct theory for horizontal layers, and they are used to "guess'" a solution for an inclined interface.

5

O_ 2

3

,

4

,
It

5

,

6

,

= 20m

=

p < 0.04I?1 p = 0.04 300 m(?} ! I ->1.5 km

FIGURE 15-17.-Model for Apollo 17 site :in which the dielectric constant varies with depth. The values of er for each frequency are shown in table 15-I. In this figure, the approximate continuous function of er is shown• Note that this interpretation is preliminary and, although the theoretical solution for each frequency is rigorous, the "solution" for the continuous variation of er with depth is somewhat intuitive at present•

%=6.5

FIGURE 15-19.-The alternate model of the electrical structure at the Apollo 17 site. A layer of thickness between 0.2k and 0.3_. is present at the SEP experiment site (left) and thins toward station 2 (right). The broken line at 300 m indicates a possible discontinuity that depth. layer is perhaps 20 m experiment site and thins in er at

layer to the exact thickness is shown clearly in figure 1 5-1 8. The basis for this type of model is best seen in the 2.1-MHz profile, which resembles the intermediate theoretical curve of figure 15-18 near the SEP experiment site and resembles the upper theoretical curve of figure 15-18 farther away. The structure that best fits this analysis is shown in figure 15-19. The

thick beneath the SEP to 15 m at station 2. In in er at a

addition, there is a hint of a discontinuity depth of approximately 300 m.

material at Taurus-Littrow, at frequencies of 1 1o 32 MHz, is approximately 3 to 4 near the surface and increases to 6 to 7 at a depth of approximately The loss tangent is less than 0.04 and possibly as 0.003. 2. The electrical structure at Taurus-Littrow simple horizontal 3. No liquid kin. layering. water is present 50 m. as low is not

in the outer

1 to 2 at fre-

4. Scattering of electromagnetic waves queneies of 1 to 32 MHz is insignificant.

5. Continuing postflight analysis of navigational data, photographs, and other data will provide location of the LRV on the EVA-2 traverse to an accuracy of a few meters. 6. Additional theoretical and scale model work is being done to solve the problem variation with depth of the dielectric the problem of dipping interface, of continuous properties and

ACKNOWLE

DGM ENTS

The experiment and equipment conceptual design was done at the Massachusetts Institute of Technology Center for Space Research. The flight hardware was designed and built by the Raytheon Company.

For the past 20 yr, astronomical interest in the cosmic dust particle has been partially dominated by a concern for the mechanical devastation imparted by meteoroid impacts or the so-called meteoroid hazard. Today, the meteoroid hazard has been accurately evaluated and found to be essentially nonexistent (ref. 16-1). Now we are witnessing an interesting period of transition for cosmic dust studies from simply determining the number and size of particles impinging on a certain area in a certain time to an astronomical interest in the nature and file source of the material. The cosmic dust particle is emerging as a much more interesting object than its larger cousin, the meteoroid, which is often seen blazing a path across the atmosphere of the Earth. Both are affected by gravity, solar wind erosion, and planetary atmospheres, but, because of its small size and consequently its high surface-to-mass ratio, the micrometeoroid is also significantly affected by solar radiation pressure, magnetic fields, electric fields, and probably the shadow or umbra of the Earth. The extraterrestrial microparticles encountered by meteorites (LEAM) experiment three distinct and interesting interstellar grains, and cometary the lunar ejecta and may be divided into classes: hmar ejecta, debris.

become molten and behave similarly to liquid masses. Secondary particles (or lunar ejecta) are ejected :radially and at high velocities from the impact site. The volume of lunar ejecta material relative to :primary particle volume and the range of velocities :for lunar ejecta are currently conjecture based on laboratory studies using hypervelocity projectiles. :Lunar ejecta mass is probably comparable, in most cases, to the mass of the impacting meteoroid. :Laboratory studies have shown that ejecta velocities may exceed the primary particle velocity, but, in general, it is assumed that a relatively small percentage of the ejecta particles have velocities in excess of _he lunar escape velocity of 2.4 km/sec; thus, the bulk of material returns to the lunar surface (ref. 16-3). The LEAM experiment intercepts ejecta particles and records information useful in establishing the history of the Moon. The manner in which interstellar particles or grains invade our solar system is depicted in figure 16-2. Our

<2.4km/sec OBJECTIVES >2.4kml ec s The lunar ejecta particle depicted in figure 16-1 is the offspring of a meteoroid encounter with the lunar surface. The Moon, hke the Earth, is continually bombarded by meteoroids traveling at hypervelocities (speeds in excess of the speed of sound in a material (ref. 16-2)). The lunar surface, unprotected by an atmosphere, receives the impact at full velocity from 2.4 to 72 km/sec. Because of the high velocity, the projectile and the immediate area of the impact aNAsA Goddard Space Flight Center. tPrincipal Investigator. 16-1 <2.4km/see FIGURE 16-1.-Lunar ejecta.

Moon

16-2

APOLLO 17 PRELIMINARY SCIENCE REPORT

Earth at1AU Orb

/_

/ /

/solar apex elocity v relative to nearlystars 20-km/sec B D FIGURE 16-3.-Cometary debris. heliocentric orbit similar to its parent; the large particulates will remain in this orbit until they are perturbed by other planets or bodies or collide with the Moon, the Earth, or other planets. These large particulates are the blazing meteoroids mentioned previously. After separation from the parent comet, the smaller particulates, micrometeoroids, behave much less predictably because they are affected by two forces: the force of gravity, which is a function of the particle mass and therefore the cube of the particle radius (4/31rr 3) and the force of solar radiation pressure, which is a function of the crosssectional area of the particle and therefore the square of the radius 0rr2). If the force of radiation pressure exceeds the force of gravity at the moment of separation from the parent comet, the particle will assume a hyperbolic trajectory, as shown for A and B in figure 16-3, and the particle will leave our solar system. If the force of gravity exceeds the force of radiation pressure at the moment of separation from the parent comet, the particle will spiral in toward the Sun very slowly under the Poynting-Robertson effect. Here again, as postulated, a second separation of particles occurs (ref. 16-7). Because of their heat capacity, the larger dust particles continue into the Sun and are absorbed, as shown by C. As the smaller dust particles approach to within a few solar radii of the Sun, they partially evaporate, and, because the relative mass or gravity (r 3) reduction is faster than the relative cross-sectional area (r2) reduction, the force of radiation pressure soon exceeds the force of gravity for the particle, and it is ejected quasi-radially from the Sun, as depicted by D. Essentially all the particles intercepted by the Pioneer 8 and 9 instruments were outgoing particles,

I

FIGURE 16-2.-Interstenar grains. Interstellar grains <40 km/sec are trapped by the solar system; those >40 km/sec pass on through. Sun and its planets are moving through the Milky Way Galaxy at approximately 20 km/sec relative to nearby stars. In so doing, our solar system passes through "clouds" of interstellar dust (ref. 16-4) with relative encounter velocities approaching and possibly exceeding 100 km/sec. Although the particles are extremely small (probably 10 -is g), their detection probability by the LEAM experiment is high because the experiment responds to the cube of the particle velocity; thus, it is extremely sensitive to high-speed particles. Two forerunners of the LEAMexperiment, in the heliocentric satellites Pioneer 8 and 9, have detected two (and possibly more) interstellar grains that are believed to be the first impact registrations of this type of particle (ref. 16-5). Because the LEAM experiment measures particle speed, radiant (or source) direction, and particle kinetic energy, the encounters by interstellar grains may be readily distinguished from encounters by other types of cosmic dust. Cometary debris is considered the most abundant component of cosmic dust within our solar system. It is generally accepted that comets are gigantic "dirty snowballs" with nuclei diameters on the order of 10 km and are principally composed of frozen mixtures of gases and liquids (ref. 16-6). Embedded in this "snowball" are solids ranging in diameters from tenths of micrometers to large boulders. As the comet approaches its perihelion, as shown in figure 16-3, it undergoes partial disintegration because of the effects of radiation pressure and spews out a tail of gases, vapors, and solid particulates. For larger comets, the tail is often visible to the eye as diffuse illumination pointing away from the Sun. Large particulate matter may separate from the parent comet and attain a

LUNAR EJECTA AND METEORITES EXPERIMENT suggesting ejected cometary fragments rather than particles in elliptical orbits (ref. 16-8). Accordingly, the LEAM experiment is skielded by the Moon from primary particle impacts during lunar night. However, the formation and presence of lunar ejecta from large meteoroid impacts are quite independent of lunar day/night conditions-a set of conditions that helps to distinguish between impacts by primary particle events and impacts by lunar ejecta. During each lunar cycle, each of three sensor systems incorporated into the LEAM experiment is alternately exposed to and shielded from impacts by these particles. The position of the LEAM experiment on the lunar surface and the associated alternated exposure and shielding feature of the sensor systems offer an opportunity for the experiment to verify Earth focusing effects (fig. 16-4). Mieropartieles that are ejected, one way or another, into our solar system will tend to be ejected radially away from the Sun. For simplicity, microparticles are shown as having parallel trajectories in figure 16-4. As they are blown past the Earth, they are perturbed toward the Earth arLd tend to focus into a concentration extending outward from the shaded side of the Earth. Thus, as shown in figure 16-4, the LEAM experiment will, once per lunar cycle, be ideally exposed to this postulated concentration and/or perturbation effects,

16-3

FIGURE 16-5.-The LEAM experiment, which responds to impacts of micropartlcleshavinga em, andlow as 10-14 g, a diameter as small as 2 × 10-s mass as a speed ashigh as 75 kin/see. experiment consists of three sensor systems: the east sensor, the west sensor, and the up sensor. Only the up and west sensors are visible in figure 16-5. The basic sensor for each array is shown schematically in figure 16-6. The basic sensor consists of a front (A) f'flm-grid sensor array and a rear (B) film-grid sensor array spaced 5 cm apart (film plane to f'dm plane) and an acoustical impact plate upon which the rear film is mounted. The performance of the sensors depends upon two basic measurable phenomena that occur when a hypervelocity particle impacts upon a surface: the formation of a plasma and a transfer of momentum. In conjunction with the following explanation of the operation of the LEAM experiment, refer to

THE LEAM INSTRUMENT The major objectives of placing a cosmic dust experiment on the Moon can readily be met by the LEAM instrument (fig. 16-5). This instrument measures the particle speed, particle direction, totalparticle energy (kinetic), and particle momentum for particles having parameters as shown. The LEAM

_

Sunlight

• . _
focusing

__ __
effect.

FIGURE 16-4.-Earth

particle (>1.0 erg); a low-energy hypervelocity particle (<1.0 erg); and a relatively large high-velocity particle (>10 -'1° g). The third type includes the majority of lunar ejecta particles. As a high-energy hypervelocity particle enters the front film sensor, it yields cosmicof dust kinetic energy high-energy hypervelocity some its particles: a toward the generation of figure 16-6 and consider three probable types of ionized plasma at the front film. Electrons from the plasma are collected on the positively biased grid (+24V), producing a negative-going pulse that is

16-4 Cosmic ust d particle

APOLLO 17 PRELIMINARY SCIENCE REPORT sensor systems that comprise the east and up sensor -IV +z4v-3.5v arrays. toThe west low-speed ejecta designed on the cally record sensor array was impacts specifimicrophone plate without has no capability a to measure consequently, this array retardation by front film; the overall LEAM experiment, shows that four particle film strips are 16-7, an by four horizontal grid vertical speed. Figure crossed exploded schematic of strips to affect arrays, creating 16 front and 16 rear f'dm 256 possible combinations, sensOrEach

output amplifier. The output signals from these grid strip and each f'dm strip cormects to a separate amplifiers are used to determine the segment in which an impact occurred. Thus, knowing what front film segment was penetrated and what rear film segment was affected by an impact, the direction of the incoming particle can be determined with respect to the sensor axis and, eventually, to the Sun.

amplified as shown (fig. 16-6). The ions from the plasma are collected on the negatively biased film (--3.5 V), producing a positive-going pulse that is amplified as shown (fig. 16-6) and pulse-heightanalyzed as a measure of the kinetic energy of the particle. As the particle continues on its path, it yields its remaining energy at the rear sensor film (and plate), generating a second set of plasma pulses and an acoustical pulse (if the momentum of the particle is sufficient). A pulse-height analysis is performed on the positive-going plasma pulse, and a peak-pulse-height analysis is performed on the acoustical sensor output as a measure of the remaining momentum of the particle, As a low-energy hypervelocity particle enters the front sensor, it yields all its kinetic energy at the front film. A pulse-height analysis is performed on the positive output signal as a measure of the kinetic energy of the particle, As a relatively large high-velocity particle enters the LEAM experiment, it may pass through the front and rear film sensor arrays without generating a detectable ionized plasma but still impart a measurable impulse to the acoustical sensor. In this event, a peak-pulse-height analysis is performed on the aeoustical sensor output pulse, An electronic clock registers the time of flight of the particle as the time lapse between positive pulses (front film and rear f'dm output signals), which is used to derive the speed of the particle. The time-of-flight sensor represents one of 256 similar

SENSOR CONTROLS An ideal sensor control is one that is exposed to the same environment as the active or main sensor. Environment encompasses electrical and magnetic radiation, thermal radiation, thermal gradients, and so forth. Controls installed somewhere in the experiment and sheltered from the total environment are ineffective. The controls used in this experiment are designed to perform, as much as possible, under the same conditions as the main sensor. An upper portion of the rear film array and a lower portion of the front film array of the east sensor system are used as controls for the plasma sensors. An epoxy resin coating covers the control grids and films, isolating them from the products of ionization caused by impacts on their area (e.g., electrons and ions generated by hypervelocity impacts on the epoxy cannot be collected on the grids or films). However, the resin coat does not constitute a shield from electrical or magnetic radiation. (Thermal noise is not an important factor in ionization sensors.) A microphone control is unique in that it is a "live microphone" attached to a separate impact plate having one-third the effective area of the main microphone plate. Thus, the control is truly exposed to the same environment as the main microphone sensor, including impacts by cosmic dust; an approximate ratio of 1:3 would be expected between impacts on the control and impacts on the main microphone sensor.

sponding to the low end of the meteoroid velocity spectrum (1 to 25 km/sec). Accordingly, when considering the sensitivities of the sensors as derived from these calibrations, the possible latent discrepansubsequent measurements in space when the sensors are exposed to projectiles of diverse density, struc-

<} <3 A-gridamplifiers r//_ _'/J I? u _ ....

ture, composition,

and higher velocities. The plasma

sens°rs resp°nd nearly that may the pr°duct mY2 "6 cies must be considered linearly t° become manifest in (rn = mass, v = velocity) over the limited particle parameter range specified previously for the laboramomentum of the particle for that same particle tory simulator. The acoustical sensors the front to film the range. The threshold sensitivity of respond sensor array to laboratory particles is 0.6 erg. Time of flight is registered for laboratory particles having l_Jnetic energies of 1.0 erg or greater. The electronics of the time-of-flight sensor are design limited to particles having velocities ranging from 2 to 72 km/sec. The threshold sensitivity of the acoustical sensor is 2 X 10-s dyn-sec (including deceleration by the front film). Hypervelocity particles passing through the front film of the sensors are decelerated in inverse proportion to their kinetic energy (for a velocity range of 1 to 20 km/sec). For particles having the minimum energy required to exhibit time of flight (1.0 erg), the deceleration is 40 percent. Deceleration drops to 5 is provided and can be initiated either automatically or by ground command. Two different formats of simulated data pulses are alternately presented by the experiment to the input of each of the amplifier systems to check the condition of the electronics and

percent for sensors. Two formats alternately calibration a the plasma particles having 10 ergs. In situ provide and the upper sensitivities of the amplifiers. Front film and a low amplitude rear film monitor pulses are high sensor pulses and pulse to sensor the lower appropriately spaced and in proper sequence to monitor the time-of-flight electronics. All accumulators advance with inflight calibration. EXPE R IM E NT ELECT RO N ICS A simple block diagram of the electronics in one of the dual (east, up) sensor arrays is shown in figure 16-8. A preamplifier receives the positive-going pulse from each A-film strip. After a gain of 3, the pulse

t t _[_L/__ I
B-grid bias l +24 V) f

Ju,

Outer grid (b) bias(-7 V) FIGURE 16-7.-Schematic of time-of-flight sensor. (a) Front sensor array. (b) Rear sensor array. CALIBRATIONS Extensive calibrations have been performed on the sensors using a 2-MV electrostatic accelerator. Unfortunately, the particles used for calibration have been

FIGURE 16-8.-Diagram of LEAMcentral electronics. divides into two separate paths. In one path, it is amplified (voltage gain Vg equals 3.2 for each input), its pulse height is analyzed, and its amplitude is recorded in the storage register. In the other path, it is amplified (Vg = 5) and fed into a threshold one-shot. The output pulse performs three functions: its origin identification is impressed directly on the storage register; it passes through the logical NOR gate and initiates the time-of-flight measurement; and it is gated back to the threshold one-shot to inhibit any other A-film pulse until the measurement has been completed, An inhibit signal to the other three films is necessary to avoid capacitative crosstalk for highenergy impact signals. The A-film pulse is pulse-height analyzed, and the results are stored in the register to await read-out, Positive-going pulses from the B-flim pass through a similar but separate electronic path, except that the B-film pulse is used to stop the time-of-flight clock. If no B-film pulse follows an A-film pulse, the time-offlight register goes to the full (63 count) state and remains full until another event occurs. Negative-going pulses from each of the grids (A and B) are amplified through separate units and identity (ID) registered as shown. For simplicity, only one set of collector amplifiers is shown in the lower center area of figure 16-8. Each film strip and each grid strip in both the front and the rear sensor arrays connects to its own separate amplifier system. The output signal from the crystal sensor (microphone), as it responds to impacts, is a ringing sinusoidal wave that increases to a maxium and then decays. After amplification in a tuned amplifier, the peak signal amplitude is used to advance the microphone accumulate, to start the register reset

LUNAR EJECTA AND METEORITES EXPERIMENT (read-out of register data), and to record the amplitude of the impulse imparted to the microphone sensor plate. The one-shot and the inhibit block shown in the microphone circuit inhibit further processing of subsequential microphone pulses until after the final pulse is placed in the storage register. Pulses from the control microphone (not shown in the block diagram) follow a similar but separate electronic course, except that no pulse-height analysis is performed and the pulses do not trigger the register reset. The sensors have been subjected to solar radiation simulators, including 3 MeV proton radiation and ultraviolet radiation. They showed no response or effects from radiation values as high as 100 solar constants, DEPLOYMENT The LEAM experiment was emplaced in the Taurus-Littrow area; its location is 43 ° east of north from the ALSEP central station at a distance of 7.5 m. As requested, the east sensor axis of the LEAM was directed 25° north of east to accommodate interstellar grains. The LEAM instrument was cornmanded "on" to operate for a period of 2 hr after deployment to verify proper performance. During this 2-hr period, two calibration commands were transmitted. The LEAM experiment responded with normal read-outs. It was commanded to the "off" mode until after lunar module (LM) ascent and detonation of the surface charges. The LEAM expertment was protected by two dust covers that were removed by ground command. One cover, designed to protect the thermal mirrors from dust contamination during LM ascent or from surface-charge detonations, was removed at a Sun angle of 130 ° (90 ° = lunar noon). A second cover, designed to protect the three sensor systems, was commanded "off" at 60 hr after lunar sunset of the first lunation. Because of the low data event rates anticipated (one event per day) for the LEAM experiment, it was essential to obtain a good measurement of the background noise or the extraneous pulse rate. Accordingly, the LEAM expertment output was recorded for periods of 60 hr of lunar day and 60 hr of lunar night with the sensor covers on. The covers were removed by a :redundant squib system that was fired by command. A monitor signal indicated successful firing of both sets of squibs. In the case of the mirror-cover removal, a

16-7

sudden decrease in the LEAM experiment temperaturesverified successful removal However, in the case of the sensor covers, there was no noticeable change of temperature conditions inside the experiment following cover deployment. That fact and several subsequent observations of temperature excursions in the experiment have prompted an extensive study into the LEAM experttrent temperature anomalies. THE LEAM EXPERIMENT TEMPE RATU R ES

Predicted temperatures for the LEAM experiment included a maximum of 146° F (336 K) at lunar noon and a minimum of -24 ° F (242 K) during lunar night. An automatic heater in the LEAM experiment turns on at 0° F (255 K) and off at 9° (261 K). The beater is designed to remain on continuously during lunar night and to keep the LEAM experiment temperatures above -24 ° F (242 K). In all cases, predicted temperatures were based on laboratory s_rnulation studies. Actual temperatures for the LEAM experiment frame plotted against Sun angle (90 ° = lunar noon) during the first three lunations are shown in figure 16-9. The plot shows that the LEAM experiment is command "off" as its temperature approaches 167 ° (348 K), an arbitrarily acceptable operating temperature based on the highest operating temperature tested in the laboratory. This acceptable temperature will be increased to probably 212 ° F (378 K), pending the results of a total investigation of the temperature anomalies. It is interesting to follow the temperature history of the LEAM experiment from the time of hmar emplacement. At a Sun angle of 130 ° during tile first lunation, the mirror covers were removed, and the temperature decreased markedly. At a Sun angle of 162°, the LEAM experiment was commanded "on," in which mode it remained throughout the first lunar night. The thermostatically controlled heater cycled on and off approximately once per 6 hr. Temperature cycling was not unexpected while the sensor covers remained on. At a Sun angle of approximately 220 ° on the first lunar niight, the sensor covers were commanded "off." No noticeable changes occurred in temperature cycling, although predictions indicated a temperature decrease and continuous heater operation. At dawn of the second lunar day, the temperature

rose rapidly to approximately 170 ° F (350 K) at a Sun angle of 15 °, and the LEAM experiment was commanded "off" and remained in the "off" mode until a Sun angle of 160 ° when it was commanded "on." The LEAM experiment remained in this mode until dawn of the third lunar day. During the second lunar night, the registered temperatures were normal (as predicted), and the heater stayed on continuously, The strange behavior of the thermal sensor during the first lunar night compared to its normal behavior during sensor the second lunar night indicated that the covers had failed to deploy fully because of

A plausible explanation for the thermal anomalies is an accumulation of lunar dust on the sensor films. There is some evidence for electrostatic levitation of dust at the lunar sunset line (refs. 16-9 and 16-10). Positively charged dust particles would be attracted to and deposited on the negatively biased fdms ; they would change the absorption/emission characteristics of a relatively large area of the LEAM experiment and cause heating. To preclude electrostatic dust accumulation at sunrise of the third lunation, the LEAM experiment was commanded "off" for a period of 75 rain so that the experiment (and films) would maintain a similar potential to the lunar surface at the LEAM experiment site. Conceivably, the dust already deposited might be removed by electrostatic repulsion at sunrise. Interestingly, the third lunation temperatures were as much as 35 ° F (19.5 K) lower than the second lunation temperatures under identi-

the extremely low temperatures. The temperature of the dust cover may have approached lunar surface temperatures. The sensor covers had presumably deployed sometime during dawn of the second lunation. The rapidly rising temperature at dawn of the second lunation is more difficult to explain,

LUNAR

EJECTA

AND METEORITES

EXPERIMENT

16-9

cal conditions (Sun angle of 15°). A few degrees after lunar noon, the temperatures for the second and the third hinations were essentially identical, It is interesting to consider further whether or not the LEAM experiment has, at least partially, verified electrostatic levitation of lunar dust. The LEAM experiment may eventually be manipulated to accommodate such studies; however, immediate plans are to operate it only at temperatures below 348 K to preserve it for the partial eclipse in June 1973. After the eclipse, the LEAM experiment will be operated continuously. Prelaunch thermal degradation analyses of the LEAM instrument show that it will operate at temperatures as high as 373 K with negligible degradation. (All electronic components for the LEAM experiment were qualified (tested) to a temperature of 257 ° F (398 K).) Meanwhile (preeclipse), the LEAM experiment will be operating during lunar nights, when conditions are ideal for the study of lunar ejecta, a major objective of the experiment.

Meaningful results from the LEAM experiment can only be derived from a long-term statistical and correlative study between primary particle events and ejecta events. In view of the relatively short-term measurement of primary particles, it seems premature to extend results beyond making a statement that, with the exception of the high temperatures, the LEAM experiment is performing normally.

RESULTS No significant results are reported at the time of this report for the following reasons. 1. The anticipated event rate from the LEAM experiment is approximately one event per day (periods of and effects from meteoroid shower activity excepted). 2. It is now assumed that the sensor covers were not removed before dawn of the second lunation and probably were removed only hours before the experi-

ment was commanded "off" during the lunar day. Accordingly, no significant real-time data were obtained during the 45-day support period, 3. All data tapes received to date contain only 150 hr of lunar day data and 620 hr of lunar night data with the LEAM experiment in the flail operating mode (the experiment in the "on" mode and the sensor covers removed).

On the Apollo 17 mission, a miniature mass spectrometer, called the lunar atmospheric composition experiment (LACE), was carded to the Moon as part of the Apollo lunar surface experiments package (ALSEP) to study the composition of and variation in the lunar atmosphere. The instrument was successfully deployed in the Taurus-Littrow valley with its entrance aperture oriented upward to intercept and measure the downward flux of gases at the lunar surface (fig. 17-1). Initial activation of the LACE instrument occurred on December 27, 1972, approximately 50 hr after sunset, and operation continued throughout the first lunar night. Sunrise brought a high background gas level and necessitated discontinaing operation during lunar daytime except for a brief check near noon. Near sunset, operation was resumed arid continued throughout the night. This sequence was repeated for the second and third lunations, The atmosphere of the Moon is very tenuous. Gas molecules do not collide with each other but, instead, travel in ballistic trajectories between collisions with the lunar surface, forming a nearly classical exosphere, Possible sources of the lunar atmosphere are the solar wind, lunar volcanism, and meteoroid impact (ref. 17-1). Of these sources, the only one amenable to prediction of the composition of the lunar atmosphere is the solar wind. Thermal escape is the most rapid loss mechanism for light gases (hydrogen and helium). For heavier gases, photoionization followed by acceleration by the solar wind electric field accounts for most of the loss. More detailed descriptions of the formation and lo.'_ mechanisms of the lunar atmosphere are given in references 17-1 to 17-4. The Apollo 14 and 15 cold cathode gage experiaThe University of Texas at Dallas. bNASA Lyndon B. Johnson SpaceCenter. tPdneipal Investigator.

ments have determined an upper bound on the gas concentrations at the lunar surface of approximately 1 X 107 moleeules/cm 3 in the daytime and 2 X l0 s molecules/cm a at night (ref. 17-2). This large daytime increase suggests that most of the lunar gases are readily adsorbed on the cold nighttime surface. Hodges and Johnson (ref. 17-5) have shown that gases that are not likely to be adsorbed at night, such as neon and nitrogen, should be distributed in concentration as a function of temperature (T-s/2) and thus have nighttime maximums. Contaminant gases originating from the lunar module (LM) or from other ALSEP experiments, or being adsorbed on surfaces in the site area could be influencing the daytime cold cathode gage readings, although such outgassing would have to exhibit very stable long-term rates because of the repeatability of the data from day to day. If the daytime maximum is a natural feature of the atmosphere, then it is probably a result of condensable gases, some of which may be of volcanic origin, while the nighttime level represents the noncondensable gases. The LACE was designed to identify the various gases in the lunar atmosphere and to determine the concentration of each species. A brief description of the instrument and a discussion of the results obtained during the first three lunations after deployment of the instrument are given in this section. INSTRUMENTATION Identification of gas molecules in the lunar atmosphere by species and determination of concentrations are accomplished by a miniature magneticdeflection mass spectrometer. Gas molecules entering the instrument aperture are ionized by an electron bombardment ion source, collimated into a beam, and sent through a magnetic analyzer to the detector system. The ion source contains two tungsten (with 1 percent rhenium) filaments, selectable by command, 17-1

17-2

APOLLO 17 PRELIMINARY SCIENCE REPORT with embedded resistors, are mounted in the ion source, enabling its temperature to be raised to 520 K for in situ outgassing. The gas entrance is pointed upward and has a dust trap around the source region that precludes the possibility of dust falling into the source itself. Voltage scan of the mass spectrum is accomplished by a high-voltage stepping power supply. The ionaccelerating voltage (sweep voltage) is varied in a stepwise manner through 1330 steps from 320 to 1420 V with a dwell time of 0.6 sec/step. Each step is synchronized to a main frame of the telemetry format. Ten steps of background counts (zero sweep voltage) and 10 steps of an internal calibration frequency are inserted between sweeps, making a total of 1350 steps/spectrum. The sweep time is 13.5 rnin. In an alternate mode, the sweep voltage may be commanded to lock on to any of the 1350 steps, enabling the instrument to monitor continuously any given mass number peak in the spectrum with a time resolution of 0.6 sec/sample. A one-step advance command is also available. The lock mode permits high time resolution monitoring of mass peaks that may be suspected to be of volcanic origin. The sweep step number, being a function of the ion-accelerating voltage, is directly related to ion mass number. Each sweep step number, in turn, is uniquely related to a main frame telemetry word. Therefore, word position in the telemetry format serves as the identifier of atomic mass number in the spectrum. Ions accelerated from the source region by the sweep voltage are collimated into a beam and directed through a magnetic field of 0.43 T. Three allowed trajectories (of radii 1.21,4.20, and 6.35 cm) through the magnetic field region define the locations of three collector slits. Figure 17-2 is a schematic drawing of the analyzer showing the major parts and the three ion beam trajectories. Thus, three mass ranges are scanned simultaneously, namely 1 to 4, 12 to 48, and 27.4 to 110 amu, termed low-, mid-, and high-mass ranges, respectively. The advantage of a triple-channel analyzer is that a wide mass range may be scanned by a relatively narrow voltage excursion. Also, the midand high-mass ranges are so related that mass 28 and 64 peaks are detected simultaneously. Therefore, in the lock mode, carbon monoxide (CO) and sulfur dioxide (SO2), which may be candidates for volcanic gases, can be monitored simultaneously. Resolution of the analyzer is set at approximately

FIGURE 17-1.-The LACE deployed on the Moon. The entrance aperture covered by a nylon dust screen is at the lower right corner of the instrument. The mass analyzer is mounted behind the front cover with the electronics in a box to the rear. The white dust cover on top protects the mirrored surface during mission activities and LSPE explosive package detonations. The instrument package measures 34 by 32 by 17 cm and weighs9.1 kg. The cable connecting the spectrometer to the central station is at the bottom of the photograph (AS17-134-20498). as electron emitters. In the normal mode of operation, the fixed mode, the electron bombardment energy is fixed at 70 eV with the electron emission current regulated at 250 _A. This produces a sensitivity to nitrogen of 5 X 10-5 A/torr, sufficient to measure concentrations of gas species in the 1 X 10-15-torr range. An alternate mode, the cyclic mode, provides four different electron energies (70, 27, 20, and 18 eV) that are cycled by successive sweeps of the mass spectrum. Identification of gases in a complex mass spectrum is greatly aided when the spectra are taken at several different electron ionization energies because the cracking patterns of cornplex molecules are strongly dependent on the bornbardment electron energy. Also, at low energy, many gas species are eliminated from the spectrum, thus greatly simplifying the task of identifying parent molecules, Two small heaters, consisting of ceramic blocks

Housekeeping circuits monitor 15 functions within the instrument (supply voltages, filament current, emission current, sweep voltage, and several temperatures). One temperature sensor monitors the ion source temperature; this value is used in data reduction. Housekeeping words are subcommutated, one each 90 main frames, thus requiring a fun spectral _;cantime to read each monitor once. The mass spectrometer analyzer, magnet, ion ,;ource, and detectors are mounted on a baseplate that

] --

Hig_ 27.4t0110amu

''

I"1

"

._/ L"_/'/

/

J
" Magnet (0.43T)

++meo, oo+oro ,ac+a+ +a

housing as shown in figure a1%1. The entrance aperture, which was sealed by ceramic cap until it was opened by the crewman, points upward, enabling the downward flux of gas molecules to be measured. Behind the baseplate is a thermally controlled box containing the electronics. The top of the box has a lnirrored surface covered by a dust cover that was commanded open after the last lunar seismic profiling experiment (LSPE) explosive package was detonated, 6 days after deployment. An arrow and bubble level on top of the package aided in proper deployment of the instrument. Calibration of the instrument was performed at the NASA Langley Research Center (LRC) in a manner similar to that of the lunar orbital mass spectrometers flown on the Apollo 15 and 16 missions (ref. 17-6). A molecular beam apparatus produces a beam of known flux in a liquid helium cryochamber. The instrument entrance aperture intercepts the beam at one end of the chamber. With _mown beam flux andionsource temperature,instrument calibration coefficients are determined. Variation of gas pressure in the molecular beam source chamber behind a porous silicate glass plug varies the beam flux and provides a test of the linearity of the i_strument response. Good linearity was achieved to as high as 5 X l0 s counts/see, where the onset of counter saturation occurs. Calibrations were done with a number of gases that may be candidates for ambient lunar gases; for example, argon, carbon dioxide (CO), CO, krypton, " 2 . neon, mtrogen, and hydrogen. Because helium . not is cryopumped at the wall temperature, no b.elium beam can be formed in the chamber; therefore, helium calibrations are not possible with this system. Sensitivity to helium was determined in the ultrahigh vacuum chamber at the University of Texas at Dallas using the LRC absolute argon calibration of the instrument as a standard for calibrating an ionization

FIGURE 17-2.-Schematic diagram of' mass analyzer. An ion beam is the inlet in the ion source from ion trajectories entering formed plenum aperture. Throe gas molecules are shown through the magnet. Electron multipliersserve as charge amplifiers. An ion pump is used to check the internal analyzer pressure before application of high voltage to the ion source or the electron multiplier electrodes, 100 for the high-mass channel at mass 82. This is def'med as less than a 1-percent valley between peaks of equal amplitude at mass 82 and 83. Krypton is used to verify the resolution, Standard ion-counting techniques employing electron multipliers, pulse amplifiers, discriminators, and counters are used, one system for each mass range, The number of counts accumulated per voltage step (0.6 sec) for each channel is stored in 21-bit accumulators until sampled by the telemetry system, Just before interrogation, the 21-bit word is converted to a floating point number in base 2, reducing the data to a lO-bit word, consisting of a 6-bit number and a 4-bit multiplier. This scheme maintains 7-bit accuracy (1 percent) throughout the 21-bit (2 × 106) range of data counts, Electron multiplier gains may be adjusted by command to a high or low value, differing by an order of magnitude. Likewise, the discriminator threshold level may be set at high or low (6-dB change) by command. The high level is u_d most of the time because it tends to minimize a spurious background noise that occurs toward the high-voltage end of the mass ranges. The internal calibration frequency read between each spectral scan verifies the operation of the counter system, the discrimination level, and the data compression circuits,

17-4

APOLLO 17 PRELIMINARY SCIENCE REPORT each channel. All the data presented in this section have been obtained from quick-look charts such as figure 17-3 and are considered preliminary at this time. Each of the major peaks in the spectrum in figure 17-3 _ be discussed in turn and will be given a tentative identification, which is essential in trying to determine its origin (native or artifact). Although many of the mass peaks observed undoubtedly arise from outgassing of the instrument or other materials at the landing site, three gases have been identified that are believed native to the Moon-helium, neon, and argon. Peaks at mass 1, 2, and 4 are identifiable in the low-mass channel. Mass 1, atomic hydrogen, is almost certainly due to dissociation of artifact hydrocarbon molecules and other hydrogen compounds, including molecular hydrogen, in the ion source. Mass 2, molecular hydrogen, results largely from outgassing of the ion source, as it is steadily decreasing with time. Eventually, a stable hydrogen peak may appear that will then probably be truly lunar hydrogen.

pressure gage. The gage calibration for helium was subsequently inferred from the ratio of ionization cross sections for helium and argon (ref. 17-7). The resulting helium sensitivity is the ratio of the callbrated gage pressure to the helium counting rate. R ESU LTS Operation of the instrument commenced approximately 50 hr after the first sunset after deployment (16 days). Performance was very good in general. All housekeeping monitors were nominal, and data were recorded on all three mass channels. Figure 17-3 is an example of a typical "quick look" nighttime spectrum recorded on a strip chart recorder in real time near the antisolar point during the third lunar night, Time, which is equivalent to voltage step number and related to atomic mass number, is plotted against the counting rate. Principal peaks are identified by mass number. The large-amplitude square pulse at the beginning and end of the spectrum in each channel is the internal calibration pulse; it is preceded by a zero

LUNAR ATMOSPHERIC COMPOSITION EXPERIMENT vapor. Even in the daytime, the mass 18 peak is not large relative to other peaks. Art upper limit of 2 X l0 T water molecules/cm 3 has beenestablishedforthe second lunar day, which indicates that little water vapor is present at the site. Mass 19 being a dominant peak is a puzzle. The H30 + ion is precluded because of the small H20 peak. Fluorine is the only other possibility. This implies that much of the mass 20 peak may be hydrogen fluoride (HF) instead of neon. The mass 20 peak issmaller thanthe mass 19 peakbya factor of 3 at night and larger by the same factor in the daytime, The origin of the fluorine is unknown, bat possibilities are the outgassing of solvents used in cleaning the instrument before flight, the outgassing of other warm areas of the site (e.g., instruments, the central station, or the radioisotope thermoelectric generator), or the natural degassing of the lunar materials. To study the neon question further, the temperature of the ion source was reduced from 270 K several times during the lunar night by turning off the fliament for periods of approximately 30 min. Reactiwttion of the filament just before scanning the mass 20 to 22 range revealed stable, net mass 20 and 22 peaks with an amplitude ratio of approximately 13, in close agreement with the solar wind isotopic ratio of neon determined by Geiss et al. (ref. 17-9). The mass 44 peak was not large enough at the: time to contribute significantly to the mass 22 peak as a doubly ionized species. A neon concentration of 7 × 10a molecules] cm 3 results, which is a factor of 20 less than that predicted by Johnson et al. (ref. 17-2). The mass 28 peak is probably nitrogen or possibly CO, and mass 32 corresponds to oxygen. These will be discussed subsequently. Peaks at mass 35, 36, 37, and 38 fall into the same category as mass 19 and 20, most likely being chlorine and hydrogen chloride (HC1). The mass 35 to 37 ratio corresponds to the

17-5

Hydrocarbon peaks at this time are all near zero amplitude. Native argon-40 (4°Ar) has been identified at other times and its diurnal behavior will be discussed later. Mass 44 is CO2, thought to originate :primarily from outgassing of the instrument. The _remaining mid-mass peaks are mainly hydrocarbons ]principally from outgassing of the ion source. The high-mass range spectrum duplicates the mid _nge below mass 44. Additional peaks of significant amplitude are the group near mass 61 and peaks at _naass78 and 85 that, as yet, are unidentified. The latter two are continuing to decrease in amplitude ,Mth time and are not considered significant. The unresolved set of peaks from 91 to 93.5 amu is probably doubly charged species in the mass 182 to 1187 range that are the isotopes of tungsten and rhenium, originating from vaporization of the filament. The group near mass 61 may be triply charged tungsten and rhenium. At this measured vaporization rote (concentration of 1 X 103 molecnles/cm 3), the useful fliament lifetime is estimated at 10 yr. The remaining peaks are again thought to be artifact hydrocarbons. Figure 17-4 is a reduced spectrum derived from law data by subtracting from each peak amplitude the counts in the adjacent valleys due to background noise and scattered ions. Small-angle scattering of ions from neutrals in the mass spectrometer is a strong function of pressure but does occur to some

103_

_}102_: "_! _110 _'

the origin of the chlorine is undetermined but is likely the same as that of fluorine. The ion source temperature reduction test was conducted for the mass 36 and 40 range also. The mass 36 and 38 peaks terrestrial chiorine isotopic ratio. As with fluorine, decreased to essentially zero; the mass 40 peak also was essentially zero, indicating a late night upper limit for any of the argon isotopes less than 200 molecules/cm a . These tests indicate that the formation of HF and HC1 is strongly temperature dependent and may arise from a reaction with hydrogen in the ion source H2 + F2 = 2HF or H2 + C12 = 2HC1.

"_! 1 10° _

I

I

10

20

30 40 5_0 60 70 Atomic mass number

I i,
[
I I I I

80

90

100

FIGURE 17-4.-Reduced spectrum taken 100 hr before sunrise of the third lunar night after deployment (16:30:00 G.m.t., Mar. 5, 1973). The solarzenith angleis 140°. Corrections have been applied for background counting rates.

17-6

APOLLO 17 PRELIMINARY SCIENCE REPORT 105

extent in daytime data where the peak amplitudes are very large, that is, more than 1 × l0 s counts/main frame in some cases. However, the corrections from scattering are typically less than 5 percent and amplitudes at this stage of data analysis is estimated to be +30 percent with some of the very small peaks having an uncertainty of a factor of 2. Most of the error comes from using the quick-look-type charts as the data source. The data are shown as counts/main frame as a function of atomic mass number. Differences between the 1 percent. The accuracy of peak frequently less than mid- and high-mass overlapping ranges are removed by averaging. Counting rates (see--1) can be obtained by multiplying each peak amplitude bythe third lunar night, given in figure days is data from 1.65. The example a few calendar 17-4 later than the spectrum of figure 17-3. At this time, the ion source temperature had been reduced from its normal operating level of 270 K to near 200 K by turning the ion source off for approximately 30 min before the measurement. The minimum nighttime total gas concentration observed to date is 4.6 × l0 s molecules/cm 3, of which nearly 20 percent is hydrogen and 25 percent is mass 19, both of which are believed to be artifact, In addition, neon and helium, both believed to be native, exist at the 15-percent level. The total gas concentration at noon of the second lunation is 4 × 10s molecules/cm 3 , of which 25 percent is hydrogen and 7 percent is mass 36 (HC1), with the remaining peaks all lower in abundance. Water vapor is 5 percent of the total. All the large peaks are believed to be dominated by outgassing of the instrument, the LM, the landing site, and so forth,in the heat of the day. Diurnal variation of helium-4 (4 He) is shown in figure 17-5, starting with first activation of the instrument on December 27 at a solar zenith angle of -155 °. Time progresses to the right through the lunar night and into the day. The first lunation continues to sunset (--90°). The complete second lunation is also shown ending at sunset (Feb. 22, 1973). The dashed curve indicates regions where the instrument was not operating. No significance is attached to the lack of tracking of the two curves because the differences are within the errors associated with reading quick-look data. Helium concentration, plotted along the ordinate, is shown to vary from approximately 2 X 103 molecules/cm 3 at lunar noon to 4 × 104 molecules/cm 3 near midnight. Because of

FIGURE 17-5.-Diurnal variation of 4He. Concentration is plotted as a function of solar zenith anglewith nighttime in the center of the figure. The distribution is typical for a noncondensable gas. the very low level of the daytime helium (only three data counts after a correction for residual helium within the instrument is made based on preflight measurements of the helium and hydrogen ratio of laboratory spectra), the night-to-day ratio of helium can only be roughly estimated to be in the range of 15to30. This distribution is generally what would be expected of a noncondensable gas; that is, one that does not freeze out at the lunar nighttime temperature of 85 to 90 K (ref. 17-5). The present measurement agrees with the daytime helium concentration of 3 × 103 molecules/cm 3 predicted by Johnson et al. (ref. 17-2). Hodges et al. (ref. 17-8) have done a Monte Carlo calculation of the distribution of solar wind helium around the Moon and found an equatorial night-to-day concentration ratio of 24, which should be slightly greater than at the 20 ° latitude of the instrument location. This distribution leads to a theoretical nighttime concentration of 4.1 X 104 molecnles/cm 3 and a daytime value of 1.7 × 103 molecules/cm 3 for the same solar wind flux used by Johnson et al. (ref. 17-2); that is, 1.3 X 107 molecules/cm 2/sec. These values are in good agreement with the measurements, considering

17-10). The helium nighttime maximum occmring significantly before dawn (the coldest surface temperature occurs just before dawn) indicates that, because of the large-scale size of the helium trajectory (115 km at night), significant helimn is lost from predawn and postsunset to the day side, from which thermal escape is a rapid loss mechanism. The 4°Ar diurnal distribution is shown in figure 17-6. The coordinates are similar to those of figure 17-5. The difference between the nighttime minimums of the three lunations is believed to be due to a continual decrease in outgassingis of the instrument with time. A significant feature the large predawn increase in concentration. The very low, late night concentration of less than 200 molecules/cm a (which must be considered to be an upper limit of 4°Ar because the peak amplitude is essentially zero) indicates that it is a condensable gas and freezes out as the surface temperature falls below its freezing point. As the dawn terminator approaches the site but before any local heating occurs, the 4°Ar peak increase is due to argon being released from the warming surface and traveling several scale heights into the night side before being adsorbed by the lunar surface. The only other peak that eMfibits this marked behavior is mass 36, probably 36Ar. When the terminator passes the site and rapid local heating occurs, outgassing of hydrocarbon peaks dominates the argon contribution to mass 40. The trough just after 90 ° may be due to local depletion of argon from the surface all along the terminator. The trough is visible because of the delay in local sunrise after terminator crossing due to topographical conditions, It may be expected that the argon concentration would decrease slowly during the day until the onset of the rapid decrease after sunset. This would reflect the typical behavior of a condensable gas. However, argon may not condense on the surface until late night when the temperature reaches its freezing point, The mass 36 peak exhibits a predawn enhancement but of a magnitude less than 10 percent of that of the 4°Ar, further supporting the evidence that the major contribution to the mass 36 peak is HC1 when the ion source temperature is at its normal nighttime equilibrium value of 270 K. An upper limit for 36Ar at night is 200 molecnles/cm 3 . AS a comparison, the diurnal concentration of CO2 (44 amu), which is a condensable gas at the night lunar surface tempera-

FIGURE 17-6. Diurnal variation of 4OAr.Coordinates are similar to those of figure 17-5. Predawn enhancement suggests boiloff of condensed gas from the warm appzoaching terminator region. Daytime increases ate due to outgassing of hydrocarbon gasesfrom the instrument, the LM, and the landing site. Carbon dioxide is shown example of a gas not showingpredawn enhancement.as an

ture, is also given in figure 17-6. This peak shows no predawn enhancement but does show a very sharp increase at local sunrise and a similarly sharp decrease at sunset. Because the instrnment is located in the Taurus-Littrow valley, local sunrise occurs nearly 8 hr after terminator crossing of the site longitude; local sunset occurs approximately 6 hr early. The lag in the CO2 decrease beyond sunset very likely results from a thermal lag in the instrument and from other equipment degassing at the site. The concentrations of two other gases, nitrogen mad CO at mass 28 and oxygen (at mass 32), are plotted in figure 17-7. Again, the coordinates are similar to those of the two previous figures. The behavior closely tracks that of CO2, with no predawn enhancement. Oxygen would be expected to freeze out at night more readily than argon because its treezing point is several degrees higher than that of argon, and the ion source temperature reduction tests indeed showed a zero amplitude peak for mass 32. The conclusion is that essentially all the oxygen is

17-8

APOLLO 17 PRELIMINARY SCIENCE REPORT maximum concentration at night. However, it is believed that the concentration of 3 X 104 moleeules]cm 3 is still at least partially artifact because of the large decrease (a factor of 4) from the first lunation to the second. This appears to be merely an outgassing rate decrease. Perhaps several lunations hence, the value may stabilize and mass 28 will become a candidate for a native gas. CONCLUSIONS the first three From the data obtained during lunations after deployment of the LACE instrument, three gases-helium, neon, and argon-have been identified as being native to the lunar atmosphere. A gases compared with several predictions is presented in table 17-I. The helium concentrations and the summary of the measured concentrations of these diurnal ratio are in excellent agreement with predictions based on the solar wind as a source, indicating that the basic tenets of the theory of a noncondensable gas are correct. However, the neon measured concentration is a factor of 20 below predictions, indicating possibly some adsorption or retention on I 0 the night side of the Moon. If true, this phenomenon is unexpected because of the very low freezing temperature (27 K) of neon. The Apollo 16 lunar orbital mass spectrometer experiment (ref. 17-I 1) did detect neon on the night side near the sunset terminator at a concentration approximately 1 X l0 s molecules/cm 3. This is approximately a factor of less Data,

artifact, and an upper limit on the lunar oxygen is in the low 102 molecules/cm a range, Conversely, mass 28, whether it is nitrogen or CO (no distinction is made at this time), would not condense at night temperatures and should have its 10sE

apredicted by R. R. Hod_es,Jr., in unpublished data. bReference 17-2. CUpperlimit; argon freezes out at night. dTotal gas concentrations from mass spectrometer during second lunar day and third lunar night after deployment; from cold cathode gageafter 10 lunations.

LUNAR ATMOSPHERIC

COMPOSITION

EXPERIMENT

17-9

than 2 higher than the present value and :iswithin the experimental errors of the measurements. This discrepancy between theory and measurement for neon is a serious problem and is one of the major be considered in the future. tasks to

Bendix Aerospace Corporation who contributed to the success of this experiment. Major contributions to the design, fabrication, and testing of the mass spectrometer were made by many of the personnel at the University of Texas at Dallas.

Argon appears to be adsorbed on the late night (coldest) part of the lunar surface as none of its isotopes are detected at this time. A significant predawn enhancement of 4oAr indicates a release of the gas from the warm approaching terminator region. The arAr and aSAr are masked by HC1 peaks at this time. Future presunrise tests with a cooled ion source should reveal the actual amounts of 36Ar and 3SAr. Clearly, argon does not behave as a noncon-

densable gas and, therefore, cannot be compared to predictions. Furthermore, 4°At probably results mainly from potassium-40 decay and subsequent "weathering" of lunar surface materials, so its presence is evidence of a truly native lunar gas. The remaining peaks of the spectra are ered to be dominated by artifact gases at The total nighttime gas density of 4.6 × cules/cm a is a factor of 2 higher than the all considthis time. l0 s molemeasured

values from the Apollo 14 and 15 cold cathode gage experiments. This is not surprising (notwithstanding errors in calibration of both instruments)because the mass spectrometer ion source is warmer than the cold discharge source of the gage and therefore would have a higher outgassing rate. However, the residual being measured by both instruments is clearly not entirely neon but a multitude of gases, including helium, As the instrument, the LM, and the landing site continue to be cleansed in the high daytime temperatures, the passage of several more lunations should produce much cleaner spectra and yield more def'mirive data on concentrations of true lunar gases or, at a minimum, reduce the upper limits now determined.

ACKNOWLEDGMENTS
The authors wish to express their appreciation to the many people at the University of Texas at Dallas and at the

18. Lunar

Neutron

Probe

Experiment

Dorothy S. Woolum, a D. S. Burnett, a_ and C. A. Bauman ,a

Primary cosmic ray protons incident on the lunar surface interact with lunar material by means of nuclear reactions, which produce neutrons as secondary products. The initial investigations of the Apollo 11 samples (ref. 18-1) showed that gadolinium in lunar materials contained isotopic wlriations that could be unambiguously ascribed to neutron capture, Such a record of neutron bombardment had not been observed previously in natural samples, either terrestrial or meteoritic, because, unlike meteorites, lunar samples are materials from a large body that is capable of developing an appreciable secondary flux of low-energy (< 1 eV) neutrons, and because, unlike the Earth, the Moon has no thick overlaying atmosphere to protect the surface materials from neutron exposure. Since the Apollo 11 mission, neutron capture on samarium-149 (149Sm) (ref. 18-2), europium-151 (ref. 18-3), bromine-79 (79Br) and bromine 81 (ref. 18-4, (barium-130 (l_°Ba)(refs. 18-5 to 18-9), tungsten-186 (ref. 18-10), cobalt-59 (ref. 18-11), and calcium-40 (ref. 18-12) also has been observed with fluences (time-integrated fluxes) that range from < 1 X 10 is to 1 X 1017 neutrons/cm 2. These data have been used to determine regolith mixing rates and depths, depths of h:radiation for lunar rocks, and accumulation rates and deposition times for core samples (refs. 18-1 to 18-7, 18-13, and 18-14). However, all these conclusions depend on knowing the equilibrium neutron energy spectrum, the neutron flux as a function of depth in the regolith, and the absolute rate of neutron production, Until recently, only the theoretical calculations of Lingenfelter et al. (ref. 18-15)and Armstrong and Alsmiller (ref. 18-16) have provided estimates for these quantities. These calculations were of sufficient complexity that it was not possible to be fully confident of the interpretation of the lunar sample acalifornia Institute of Technology. "_Principallnvestigator.

data, and, for this reason, the lunar neutron probe experiment (LNPE) was performed. The LNPE was designed to obtain a direct in situ experimental measurement of neutron capture rates as a function of depth in the regolith, as well as to retrieve some information about the energy distribution of the equilibrium neutron flux. This section contains a complete description of the lunar neutron probe and a preliminary account of the data obtained to date. Preliminary results also have appeared in the abstracts for the Fourth Lunar Science Conference (ref. 18-17). All data processing for the LNPE occurs after the return of the instrument to Earth, and complete processing of the data will require several more months. The account contained in this section should be viewed as a progress report on the first stages of data processing. EXPERIMENT Principle DESCRIPTION Detection

oI Neutron

The LNPE is in the form of a rod that is inserted into the lunar regolith to permit the measurement of neutron capture rates to a depth of 2 m. The LNPE contained two passive particle-track-detector systems: (1) cellulose triacetate plastic (Triafol TN) detectors were used in conjunction with boron-10 (1o B) targets to record the alpha particles emitted by neutron capture on l°B; and (2) muscovite mica detectors were used to detect the fission fragments resulting from neutron-induced fission in uranium-235 (23sU) targets. In addition, 0.46-mm-thick cadmium absorbers were included at two locations in order to obtain information about the neutron energy spectrum. The cadmium strongly absorbs neutrons that have energies below 0.35 eV; consequently, only the fraction of the neutron population above this energy will be measured at these locations. Further spectral information will be available from analyses of 18-.1

18-2

APOLLO

17 PRELIMINARY

SCIENCE

REPORT

krypton-80 and krypton-82 produced by bromine neutron capture in potassium bromide (KBr) contained in three evacuated capsules inserted in the probe. The bromine neutron capture occurs at energies (10 to 100 eV) that are significantly higher than those for 23sU and l°B. Krypton analyses will be performed by Marti and Osborne of the University of California rately. (San Diego), and results will appear sepa-

Instrument

Description

The LNPE was taken to the Moon in a deactivated mode, activated and deployed during the first period of extravehicular at the end of activity (EVA-I), then deactivated EVA-3 and returned to Earth for materials. Figure view of the lunar

processing of the track detector 18-1 is a schematic, cross-sectional

neutron probe showing the layout of the targetdetector systems and illustrating the mechanism of activation and deactivation. The I°B targets are mounted on one-half of the outer circumference of a ...-'235U f0il covering window....

_ Activated IIFITI1Mica

detector

_ Deactivated

_

Centralrod

Boron _ Rib cage FIGURE 18-1.-A schematic, cross-sectional view of the lunar neutron probe, illustrating the disposition of the targets and detectors in the activated (on) and deactivated (off) modes. The boron targets and mica detectors are mounted on the central rod; the plastic detectors and uranium targets are mounted on the rib cage. When activated, the targets face their respective detectors; when deactivated, the target and detector systems are 180 ° out of alinement.

FIGURE 18-2.-A portion of the central rod, showing the boron target half cylinders mounted on it. The dark, circular area contains one of the uranium-238 (238U) metal disks masked to a diameter of approximately 1 mm. The 23sU was used to provide fiducial marks in the plastic detectors for verifying activation and deactivation. The boron targets are 7.5 cm long.

LUNAR NEUTRON PROBE EXPERIMENT central rod (fig. 18-2). The mica detectors are fixed on flats milled on the opposite side of the central rod (fig. 18-3). Concentric with and surrounding the central rod is an open, cylindrical frame structure (rib cage) around which sheets of the plastic detector are wrapped. The 23sU targets are mounted in discrete positions over windows in the rib cage (fig. 18-4). A continuous, black-anodized tube (not shown in fig. 18-1) is used as a casing to enclose and protect the target-detector systems. The probe is activated and deactivated by a 180 ° rotation of the central rod with respect to the rib cage (fig. 18-1). In the activated configuration, the uranium-mica and the boron-plastic target-detector pairs are brought into alinement. In the deactivated configuration, the uranium and boron targets are adjacent and the mica and plastic detectors likewise. In the latter configuration, particles emitted from the target surfaces cannot enter the respective detectors; thus, the probe is deactivated. The activation and deactivation mechanism was necessary to prevent the accumulation of background events from neutrons produced by cosmic ray interactions in the spacecraft and by the plutonium-238 power source for the Apollo lunar surface experiments package (ALSEP), the radioisotope thermoelectric generator (RTG), which is a strong neutron source (_7 × 107 neutrons/sec). Figure 18-5 is a schematic, cutaway view of the LNPE showing the manner in which the various detectors were deployed along the length of the probe. For reference, the theoretically predicted depth (in units of grams per square centimeter) profile of the neutron capture rate is plotted. To permit accurate definition of the flux profile, the length of the probe was chosen to be 12m, a depth which is well below the theoretically predicted peak of the profile (_ 150 g/cm2). The boron-plastic detection system was essentially continuous along the full length of the probe. As shown in figure 18-5, 16 uranium targets and mica detectors were mounted at eight discrete locations along the probe. The FIGURE 18-3.-A photograph of two rectangular mica detectors mounted on fiats in the central rod. The mica detectors are 1.8 cm long. Also included at this location is one of the circular temperature sensors.None of the four circular indicators had turned black, indicating that the temperature never exceeded 333 K. The photograph was taken during the photodocumentation of the LNPEafter the Apollo 17 mission.

18-3

18-4

APOLLO

17 PRELIMINARY

SCIENCE

REPORT

FIGURE 18-4.-A portion of the rib cage during the early stages of the assembly of the probe, before the mounting of the plastic detectors. Visible are one of the open windows and a window covered with a _su metal target that has, in turn, been completely covered with aluminum foil to prevent the re_stration of alpha particles in the plastic detectors when they are wrapped onto the fib cage, The windows are 1.2 cm long.

uranium-mica target-detector pairs were mounted with uniform separations in the lower half of the probe but were closely spaced and concentrated toward the top in the upper half of the probe. This arrangement was chosen for two reasons. First, the temperature of the probe was expected to be highest near the surface, and the investigators were concerned about thermal annealing of the tracks in the plastic detectors. Fission tracks in mica are not annealed even at peak lunar surface temperatures; thus, if data were lost in the plastic at the top of the probe, the mica data would still provide the near-surface record. Second, from theoretical predictions, the lowest track densities were expected near the surface, and results from the Apollo 16 cosmic ray experiment (ref. 18-18) suggested that these densities might be quite

,-_

x 103

LNPE handle

Theoretical profile

'
[_==

Upper LNPE
== == = _¢,*'Aml ?== == == = =1_,-_'=

/

Depth,g/cm 2 i== 235U-mica detection ystem s * 238Ufiducialsystem KBrcapsules rez_Cadmium-wrapped sections FIGURE 18-5.-A schematic view of the lunar neutron probe showing how the various targets and detectors are distributed with depth and including the theoretically predicted t_ack density versus depth curve. The I°B targets and plastic detectors (not shown) are essentially continuous along the entire length of the probe.

LUNAR NEUTRON PROBE EXPERIMENT low. At such densities, mica detectors give more reliable results than plastic detectors. Also displayed in figure 18-5 are the locations of the two cadmium absorbers near the bottom and middle of the probe. A 0.46-ram-thick cadmium sheet was wrapped around the rib cage over the plastic detector at each site (fig. 18-6). The evacuated KBr capsules were inserted at the top, middle, and bottom of the probe, as shown. In addition, three point sources of uranium-238 (23su') were mounted near the bottom, middle, and top of the probe in flats :milled on the side of the central rod on which the l°B targets were mounted (fig. 18-2). The reason for including the point sources was twofold. The alpha particles emitted by these point (1 to 2 mm) sources registered in the plastic detectors only while the probe was activated and thus provided fiducial marks From which the proper activation of the probe can be verified. Also, from the track densities and the appearance (length, width, etc.) of the 238U alphaparticle tracks, it will be possible to determine whether the tracks in the plastic detectors have been thermally annealed during and after the activation and the lunar surface exposure. In wrapping the plastic sheets on the rib cage, an overlapping second layer was placed over the window areas, primarily to secure the plastic to the rib cage better. Because the second layer is never exposed to any of the targets, however, four small portions of plastic in this outer layer were preirradiated with a known dose of 238U alpha particles to provide an additional check on thermal annealing in the plastic. Further, the areas of the plastic detectors in this second layer that are not preirradiated provide a continuous record of background events resulting from cosmic rays and tracks produced by nuclear interactions (recoils) of the RTG fast neutrons with the plastic. Based on analyses of small pieces of the Triafol TN plastic carried on the Apollo 15 spacecraft, the background from cosmic ray alpha particles and heavy ions was expected to be negligible. The Apollo 16 cosmic ray experiment results had suggested that the plastic would register tracks from fast-neutron interactions (ref. 18-18). Separate experiments using both californium-252 and

18-5

FIGURE

18-6.-A

portion

of

one

of the

fully

assembled

rib

cages. Two plastic detectors and one of the cadmiumwrapped areas are shown. The cadmium cylinder is 7.5 cm long.

18-6

APOLLO 17 PRELIMINARY SCIENCE REPORT

plutonium-beryllium (Pu-Be) neutron sources have shown that fast (MeV) neutrons produce tracks with an efficiency of _ 2 × 10 -6 . For this efficiency, an RTG fast-neutron background track density of _ 150 tracks/cm 2 is expected in the plastic during the flight to the lunar surface. This value is not large compared to predicted t°B alpha-particle track densities (> 1000 tracks/cm 2). To provide an actual measurement of the maximum temperature exposure of the LNPE, temperature indicators were fastened to flats in the central rod at four positions along the probe (fig. 18-3). Each temperature indicator contained four separate temperature-sensitive compounds that irreversibly turn black at 140 °, 160°, 180 °, and 200 ° F (333, 344, 355, and 366 K), respectively. The completely assembled flight unit is shown in figure 18-7. For convenient stowage on the spacgcraft, the LNPE was fabricated in two 1-m-long sections that could be activated separately. The upper section (on the right in fig. 18-7) was activated by depressing a bar on the large handle at the upper end o and rotating the handle 180 . The lower section was activated by removing the dust cap at its upper end and using it as a tool to rotate the central rod. The center rod was spring loaded to snap into one of two stable configurations differing by a 180 ° rotation. After activation, the two sections could be coupled for deployment by simply screwing the two sections together. Targets and Detectors _.:_:: :_ ......

:;_ !ii_

The boron targets were prepared with a process especially developed for this experiment. The l°B is vacuum deposited as metallic boron by the thermal cracking of diborane onto 0.05-mm-tttick tantalum half cylinders. The deposition temperature was approximately 1073 K. The l°B targets were made "infmitely thick"; that is, they were deposited to an average thickness of 1.4-+ 0.2 mg/cm 2, which is greater than the range of the 1.6-MeV alpha particles emitted with neutron capture on _°B. Each target was FIGURE 18-7.-The assembled flight unit of the lunar neutron probe. The upper section, with the probe handle at the top, is on the right. The lower section with its removable dust cap is on the left. Coupling of the two sections is accomplished by screwingthe lower and upper units together after removingthe dust cap. Each section is approximately 1 m long.

LUNAR NEUTRON PRO BE EXPERIMENT tested individually using a Pu-Be neutron source. The thickness and uniformity of several target,,; also were checked by alpha backscattering techniques using the California Institute of Technology tandem Van de Graaff accelerator, The 23sU targets were cut from 0.025-ram-thick foil sheets of 99-percent enriched 23sU, cleaned in nitric acid (HNO3), and then coated with a 30-nm-thick layer of silver to prevent oxidation and corrosion of the uranium. A film of this thickness produces negligible attenuation of the emitted fission fragments. Alpha-particle counts were determined for each target to verify the relative quality and unifortuity of the targets used. Experimentation with Triafol TN has shown that this plastic is somewhat nonuniform in its track registration properties. Exposure to monoenergetic accelerated alpha particles indicates an energy registration interval from _0.25 to 2.5 MeV, which probably applies to most samples. However, some batches of plastic show considerably reduced sensitivity, which is critically dependent on whether the irradiations are performed in air or in vacuum. One batch in particular will not register alpha particles in vacuum but does in air. These phenomena presumably reflect the critical role played by oxygen in track formation in plastic. This oxygen influence has been studied previously by Monnin (ref. 18-19) and by Crawford et al. (ref. 18-20). Because of the lack of uniformity, the registration properties of representative samples of the plastic used for the flight unit were determined by using vacuum neutron irradiations of the plastic samples exposed to a _°B target, The registration of the plastic was uniform to better than -+ 10 percent over an area of _ 0.3 m 2. Comparison of air and vacuum registration shows a small vacuum effect, with the vacuum registration efficiency being less by approximately 12 + 3 percent, Before incorporation into the probe, the plastic and mica detectors were preannealed to remove any possible background tracks. Preannealing of the mica was particularly important because muscovite, like most natural micas, has a nonnegligible density of fossil fission tracks from the spontaneous fission decay of trace uranium impurities. The mica was annealed at 903 K for 3.5 hr; the plastic, at 389 K for 9 days. In addition to being preannealed, the mica was pre-etched 4 hr in 48 percent hydrofluoric acid (HF) at room temperature and then silver coated (_ 30 Tun thick). Because normal etching time for

18-7

fission tracks in muscovite mica usually is 20 min to 1 hr, any small, shallow pits left after the preannealing appear as huge, shallow troughs and cannot be confused with the smaller diameter lunarneutron-induced fission tracks. The silver coating was applied to monitor any possible flaking of the prime detecting surface of the mica. The coating does not affect the registration properties of the mica. The techniques used for preparing the detectors fi3r data analysis are standard. The mica detectors are f.xst desilvered in a 35-percent solution of HNO3 and then etched in 48 percent HF for 25 min or 1 hr. Data reported in this section are from samples etched 25 rain and scanned in an optical microscope at 630 X magnification. Samples etched 1 hr have larger tracks and are scanned at a lower (500 X) magnification. When a sample was etched for 25 rain and counted, then etched further to 1 hr and recounted, the results agreed within one standard deviation. The plastic detectors are etched in a bath consisting of five parts 12 percent sodium hypochlorite and seven parts 6.25N sodium hydroxide at 313 K. The alphaparticle tracks in Triafol TN range only to approxiraately 4/tm in length and, consequently, are scanned at amagnificationof 1000×. The LNPE Deployment The deployment of the LNPE was nominal. The LNPE was retrieved from the modularized equipment stowage assembly (MESA) where it was stowed and was loaded on the lunar roving vehicle at the beginning of EVA-1. To prevent overheating, the two sections were kept in a thermal bag during the EVA activities before actual deployment. Following the ALSEP deployment, the deep drill corestem sample was acquired at a site approximately 40 m north (ref. i[8-21) of the ALSEP central station and the RTG power source. After the recovery of the deep core, the two LNPE sections were removed from the thermal bags, activated, coupled, and emplaced in the deep drill corestem hole. The insertion was made after first passing the probe through the hole in the I?readle used for recovering the deep core. The treadle was used because, in retrieving the deep core, the top of the hole had been widened; thus, the possibility existed that the probe would drop too far into the hole to be retrieved. Full emplacement of the LNPE was achieved manually. The deployment site was in a :_hallow depression and behind a meter-sized rock,

18-8

APOLLO 17 PRELIMINARY SCIENCE REPORT 14o0 _ 1200 _ .,_',_ _

which should have provided additional shielding from the RTG neutrons. To above the surface was covered the probe protruding prevent overheating, the top of with the thermal bag during exposure.and returned was The LNPE to recovered, decoupled, deactivated, accruing 49 hr of exposure. the The LNPE has been returned end of EVA-3, after lunar module at the very to the investigators and has been disassembled. The targets and detectors are in excellent condition; no flaking was observed in the mica detectors or on the boron targets. Furthermore, the temperature indicators showed that the probe temperature did not reach 333 K. R ESU LTS Depth Profile of the 23s U Fission Rate

_ 800 - 10o0 _ 600 __ _, 4o0i __ 200 /

O/_eTheoretical rofile"" p

%
_\
I ]

]

J

1o0

2o0
Depth, g/crn2

30o

40o

To date, only the mica detectors have been examined. The processing of the plastic detectors has been delayed in order to explore a suggestion 1 for processing the plastic that may produce better deycleped tracks, which would be easier to recognize and count, Figure 18-8 is a plot of the experimental data (shown as points in the figure) from nine of the 16 mica detectors; at least one mica from each of the eight distinct pairs located along the probe was sampled. The error bars are one standard deviation based solely on counting statistics. The depths in grams per square centimeter were calculated from the measured bulk densities of the samples in the deep drill core sections. 2 The solid curve in figure 18-8 is the theoretical profile of the neutron flux (ref. 18-15), which has been normalized to the measured track density at 150 g]cm 2. No adjustment of the depth scale has been made. Because the neutron energy spectrum below approximately 1 eV is expected to be independent of depth except for the first few centimeters, the theoretical profile defines the depth dependence of the neutron capture rate for all elements that capture neutrons in this energy region, The depth prot'de assumes a uniform chemical composition corresponding to Apollo 11 sample 10084; however, from the work of Lingenfelter et al. I MichelMonnin, private communication,1973. 2 D. Carder, G. Heiken, and S. Nagel, private communiontion, 1973.

FIGURE 18-8.-Comparison of the raw fission track data from the mica detectors and the neu_zonflux theozetieal profile (tel. 18-15), which has been normalized to the measured track density at 150 g/cm 2. The error bars on the data points are one standard deviation, based solely on counting statistics. The depth scale has not been adjusted.

(ref. 18-15), it can be argued that the profile would not change significantly if a chemical composition corresponding to samples from any other site had been chosen instead because the depth profile for the flux is determined only by the depth distribution of the neutron production rate and the neutron moderating properties of the soil. Only the latter depends on the chemistry, being governed by the most abundant elements, silicon and oxygen, the abundances of which do not vary appreciably from site to site on the Moon. If the chemical composition in the deep drill corestem sample is not homogeneous and if the concentrations of either the major-element neutron absorbers (primarily titanium and iron) or the trace-element absorbers (for instance, the rare-earth elements) vary significantly, the variations will have to be considered in the final comparison between the theoretical and experimental profiles. The deep core materials, once analyzed, will provide the information necessary to construct the appropriate theoretical curve for comparison. Also, after the postflight calibration data analyses have been completed, corrections for possible minor differences in the uranium-target efficiencies can be applied. These corrections have not been made in the data presented in figure 18-8. An additional small correction to the experimental profile may be necessary for the distortion caused by the finite size of the drill-stem hole in which the probe was inserted.

LUNAR NEUTRON PROBE EXPERIMENT Based on the results of a field simuh, tion experiment, significant corrections for background from the RTG neutrons probably will not be required; however, quantitative estimates for this correction are not ct, rrently available. The rapid decrease of the observed track densities near the surface _dso suggests that the RTG background is small because the track density prof'fle produced by RTG neutrons is expected to peak much closer to the surface; this would cause the curve of the observed track densities to flatten out as it approached the surface, Despite these qualifications, if the current data are accepted at face value, the trend of the data points is in very good agreement with the theoretical profde. Absolute Value of the 2asU Fission Rate

18-9

substitution is necessary because two fragments are emitted in the fission of 23sU but only one alpha particle is produced with neutron capture on 1°B. Data are not yet available for plastic track detectors; the following discussion applies only to the uraniummica system. The factors in equation (18-1)can be evaluated in several ways, but only one method, in which f, R, and G are evaluated independently, has been used so far. The value of R is expected to be close to the radiochemically determined fission-fragment range in metallic uranium (10 × 10 -3 g/cm 2 , ref. 18-22). However, as indicated by the studies of Reimer et al. (ref. 18-23), the range value appropriate for equation (18-1) may be slightly less than measured radiochemically. Based on natural-uranium/mica detectors irradiated in 21r geometry in a well-thermalized neutron flux, monitored by goldfoil activation, an effective range of 8.4 X 10 -3 g/cm 2 is obtained for the standard etching and scanning conditions. The following two methods have been used to determine G. 1. The neutron probe was assembled with some mica samples mounted in direct contact with the standard configuration on the center rod fiats. After neutron irradiation, G was calculated from the ratio of the fission track densities in the mica samples on the center rod to the mica samples irradiated in 27r geometry. 2. The probe was assembled with pieces of the plastic detector mounted on the center rod fiats and also in contact with the uranium targets. The value for G was calculated from the ratio of the uranium alpha-particle track densities in the center rod plastics to those in contact with uranium, as in (1). Good agreement was found between the G values obtained (0.60 -+0.02) by using these two methods. To eliminate self-absorption effects, natural uranium was used for all determinations of R and G values. At present, the principal uncertainty in the absolute fission rate lies in the value of f. The determination of f is more complicated than the determination of the other factors in equation (18-1) because the value of f varies with neutron energy. However, it is possible to estimate f using only the general features of the lunar neutron energy distribution without depending on the accuracy of the theoretical energy spectrum. The calibration proce-

The relationship between the measured track density p (tracks/cm 2) in the mica detectors and the neutron fission rate n (fissions/g(Z3sk0-sec) in the uranium targets is given by f0 = n _ 8r (18-1)

where T is the exposure time of the probe, R is the mean range in grams per square centimeter of a single fission fragment in metallic uranium, and G is a dimensionless constant defining the geometrical elficiency of the mica detectors compared to 27r geometry (G < 1). The quantity of R/2 is the average depth from which fission fragments produced in the uranium will register in a mica detector placed on the surface of the uranium (27r geometry). In the actual experimental configuration, because of the necessity for the on-off mechanism, the targets and detectors were not in contact; G is the factor that accounts for the decrease in detector efficiency caused by the required separation. A correction for self.absorptionf must be applied because the target materials in the neutron probe are strong neutron absorbers; consequently, the neutron flux and hence the measured track densities in the presence of the probe are somewhat depressed compared to their values in the absence of the probe materials. As defined in equation (18-1), f is a dimensionless constant and must have a value _> 1. The values for f, R, and G are obtained from laboratory calibration experiments, Equation (18-1) is also applicable to the boron-plastic system if the factor R/2 is replaced by R/4. This

dures used to date have been designed to determine f using neutron energy spectra that are harder and softer than the lunar spectrum and thus bracket the lunar self-absorption factor, Lunar material is a good absorber of low-energy neutrons; thus, the neutron energy spectrum in the region below 1 eV will be significantly shifted to higher energies compared to the Maxwell-Boltzmann distribution that would be expected if the low-energy neutrons were able to come into thermal equilibrium, This shift is shown, for example, by the measured ratio of samarium to gadolinium neutron capture in hmar samples, which is much higher than the ratio expected for a thermalized neutron energy distribution (ref. 18-2). Because neutron self-absorption is greatest at those energies at which the fission cross sections are large and because the 2asU fission cross section ls highest at low neutron energies, the self-absorption factor obtained in an irradiation with a thermal spectrum will be an upper limit for the value of f that is appropriate for the lunar data. A calibration irradiation was performed in a well-thermalized neutron flux, and fwas determined by comparing track densities from the actual 2asu targets with those from much more dilute 2asu targets, consisting of either natural uranium (0.72 percent 23sU) or depleted uranium (0.409 percent 23sU), in which the self-absorption was negligible, The 23sU targets were mounted at one end of the probe in the actual experimental configuration, ineluding I°B targets on the center rod. At the other end of the probe, isolated from any I°B targets, the natural- and depleted-uranium targets were similarly mounted. The measured value off thus includes the effect of the _°B targets on the 23sU fission rate as well as the effect of the 23sU foils themselves. A self-absorption factor of 1.37-+ 0.04 was obtained. Thus, the value forfhas been bracketed:f_<l.4and f_> 1 (by definition). Consequently, f= 1.2 + 0.2 has been adopted as the self-absorption factor appropriate for the lunar 2asU fission rate. Additional calibration using a harder flux will yield a somewhat more precise value forfby providing an experimental lower limit, Using the values of R, G, andfgiven previously, a _3sU fission rate of 3.5 + 0.6 fissions/g(2asU)-sec is obtained at a depth of 150 g/cm 2 , which approximately corresponds to the peak of the neutron flux proffile,

tl°F(E)_(E)dd_

(18-2)

where N is the number of 2aSU atoms per gram, oFis the fission cross section for 23su, E is neutron energy, _b(E) is the energy distribution of the neutron flux as calculated by Lingenfelter et al. (ref. 18-15), and S is the ratio of the cosmic ray neutron production rate for the 2 days when the neutron probe was deployed on the lunar surface to the average rate over the 11-yr solar cycle. Although S can be estimated from terrestrial atmospheric neutron monitor data, this estimation has not yet been made. For the present, S = 1 should be a reasonable estimate because the Apollo 17 landing occurred at a time roughly between solar maximum and minimum and because neutron monitor counting rates do not show longterm time variations larger than approximately 20 percent. The value of _b(E) calculated for the composition of Apollo 11 soil sample 10084 at a temperature of 200K has been used. This value is a reasonable approximation to the Apollo 17 conditions, but the actual Apollo 17 chemistry and temperature will be used in the final comparison. The theoretical value obtained for 150 g/cm 2 is 3.2 fissions/g(23sU)-sec; thus, within the present expedmental uncertainties, agreement is obtained between the experimental and theoretical capture rates. However, it should be emphasized that this agreement may be somewhat fortuitous. In particular, no reliable estimate of the error in the assumption ofS = 1 is available currently. CONCLUSIONS Although the analysis is stiil at a preliminary stage, it appears that good agreement exists between the experimental results and the theoretical calculations of Lingenfelter et al. (ref. 18-15). If the subsequent refinement of the experimental data and of the theoretical predictions conf'trms this agreement, the conclusions drawn previously from lunar sample data and the theoretical calculations can be accepted with some confidence. The following discussion is based on this assumption. Some justification is required for the assumption that agreement between the theoretical and experi-

LUNAR NEUTRON PROBE EXPERIMENT mental capture rates for 23sU (or l°B) implies agreement for other elements. This assumption probably is good for gadolinium-157 (lSTGd) and 149Sm because these nuclei capture neutrons in an energy range similar to that of 23sU or lOB; however, the assumption is less valid for such nuclei as la°Ba or _9Br, which capture neutrons at higher energies. This argument is illustrated in figure 18-9, in which the fraction of neutron captures that occur at different neutron energies for these nuclei is shown. These curves were calculated using the neutron energy spectrum of Lingenfelter et al. (ref. 18-15). The curves for lSTGd, 1°B, and 23sU are qualitatively similar and peak at much lower energies than the curve for 13°Ba or 79Br, although 23Su has a distinct contribution (-_ 20 percent) from neutron capture at energies higher than 10 eV. In all cases, a neutron energy spectrum must be assumed in order to calculate the relative capture rates of 2asu or 1°B to other nuclei. Figure 18-9 shows that the uncertainties in the neutron energy spectrum are less important for lSTGd than for _3°Ba or _gBr. The _gBr capture rate will be measured directly from the KBr capsules contained in the LNPE. The gadolinium and samarium isotopic variations measured in the Apollo 15 deep core sample showed a distinct peak at _ 200 g/cm 2 , which is approxi-

18-11

mately 50 g/cm 2 higher than the theoretically predicted maximum (ref. 18-15). The peaked distribution unambiguously indicates that this area of the lunar surface has remained uncratered for a relatively long period (_ 500 X 106 yr). The LNPE data show that the difference between the observed and the theoretical peak depths cannot be ascribed to the uncertainties in the theoretical flux profile but, instead, must reflect a recent (_<50 × 106 yr) deposition of _ 50 g/cm 2 of material at this site. The deposition may have resulted from a single event or from a large number of events. Even after allowing for the relatively large uncertainties that currently exist, the LNPE data place strong constraints on the interpretation of the measured neutron fluences in lunar soil samples. As discussed extensively in previous papers (refs. 18-1, 18-3, and 18-13), the observed fluences in soil samples from all Apollo missions are much lower than expected for material that has resided in the upper few meters of the lunar surface for times corresponding to the age of the site. One interpretation is that the low fluences reflect deep mixing of the lunar regolith on a 1 X 109-yr time scale by which the observed fluences for surface soil samples are diluted. However, the required mixing depths calculated from this model using the theoretical lSTGd capture rate are high; for example, approximately 15 m for Apollo regolith depths estimated from photogeology (ref. 11, a depth LNPE data roughly 3that this factor-of-3 18-24). The which is indicate times greater than theoretical capture rates used previously. Thus, regolith depth of 5 m is accepted as correct for difference cannot be ascribed to inaccuracies in Apollo 11 site, it must be concluded that previously mentioned uniform mixing model is if a the the the not

--_

A

130Ba' 79Br

157Ga _. g _ -_
2"

valid and that the lunar regolith has not been well mixed to a depth of 5 m over a time scale of that the upper portions least irradiated material approximately 1 × 109 of the regolith must irradiated material. of the regolith contain the and Instead, it would portions yr.